B&B and Vacation Rentals
B&B and Vacation Rentals
B&B and Vacation Rentals
Choose the right place for you

FACILITIES

  • Wi-Fi
  • Non Smoking Only
  • Pets Allowed

REVIEWS

  • 9+ Exceptional
  • 8+ Fabulous
  • 7+ Very Good

DISTANCE FROM CENTRE

  • Less than 1 km
  • Less than 3 km
  • Less than 5 km

Holiday rental deals in Krems an der Donau

We have selected the best vacation rentals in Krems an der Donau. Save money with Bluepillow by comparing the best deals from major travel websites in Krems an der Donau

  • Weingut Bäuerl

    • Hotel
    9.6 Exceptional (9)
    With a stay at Weingut Bäuerl in Durnstein, you'll be just steps from Wachau and Danube River. This apartment is 1 mi (1.7 km) from Stifskirche and 1.1 mi (1.8 km) from Burgruine.
    Make yourself at ...
  • Winzerhof & Gästehaus Stöger

    • Hotel
    With a stay at Winzerhof & Gästehaus Stöger in Durnstein, you'll be within a 5-minute walk of Wachau and Chorherrenstift. This guesthouse is 0.1 mi (0.2 km) from Danube River and 0.2 mi (0.2 km) from ...
  • Deluxe Apartment With Private Patio and Terrace in the Historic Centre of D Rnstein

    • 2 Guests · 2Bedrooms
    With a stay at this apartment in Durnstein, you'll be a 1-minute walk from Wachau and 13 minutes by foot from Burgruine. This apartment is 0.3 mi (0.4 km) from Danube River and 0.2 mi (0.3 km) from Chorherrenstift. ...
  • Deluxe Apartment With Elevator in the old Town of Krems With Private Parking

    • Hotel
    10 Exceptional (2)
    With a stay at this apartment in Krems an der Donau, you'll be just steps from Wachau and Sgraffitohaus. This ski apartment is 1.4 mi (2.3 km) from Danube River and 0.2 mi (0.3 km) from Pfarrkirche.
    ...
  • Deluxe Loft With Terrace in the Historic Centre of Krems

    • Hotel
    With a stay at this apartment in Krems an der Donau, you'll be just steps from Wachau and Sgraffitohaus. This apartment is 1.4 mi (2.3 km) from Danube River and 0.2 mi (0.3 km) from Pfarrkirche.
    ...
  • Deluxe Apartment With Elevator in the Historic City Centre of Krems

    • Hotel
    With a stay at this apartment in Krems an der Donau, you'll be just steps from Wachau and Sgraffitohaus. This apartment is 1.4 mi (2.3 km) from Danube River and 0.2 mi (0.3 km) from Pfarrkirche.
    ...
  • Apartment With Terrace and King Bed in Krems City

    • Hotel
    With a stay at this apartment in Krems an der Donau, you'll be a 1-minute walk from Wachau and 8 minutes by foot from Sgraffitohaus. This apartment is 0.7 mi (1.1 km) from Danube River and 0.5 mi (0.8 ...
  • Danube Beach House With D Rnstein Panorama

    • Hotel
    With a stay at this apartment in Rossatz-Arnsdorf, you'll be just steps from Wachau and Danube River. This apartment is 4.8 mi (7.7 km) from Kunst Halle Krems and 4.8 mi (7.7 km) from State Gallery of ...
  • Deluxe Apartment With Terrace and Parking in the Historic City Centre of Krems an der Donau

    • Hotel
    10 Exceptional (3)
    With a stay at this apartment in Krems an der Donau, you'll be within a 5-minute walk of Wachau and Sgraffitohaus. This apartment is 1.3 mi (2.1 km) from Danube River and 0.2 mi (0.3 km) from Pfarrkirche. ...
  • City Gate Kremser Tor With Roof Terrace Garden and Parking lot

    • 4 Guests · 4Bedrooms
    With a stay at this apartment in Durnstein, you'll be just steps from Wachau and Stifskirche. This apartment is 6.9 mi (11.1 km) from Danube River and 0.2 mi (0.3 km) from Burgruine.
    Make yourself ...
  • Winzer Penthouse Donaublick mit Dachterrasse im Malerwinkel von D Rnstein

    • 4 Guests · 3Bedrooms
    4 Pleasant (2)
    With a stay at this apartment in Durnstein, you'll be just steps from Wachau and Danube River. This apartment is 0.1 mi (0.1 km) from Stifskirche and 0.3 mi (0.5 km) from Burgruine.
    Make yourself ...
  • Deluxe Apartment With Balcony Parking and Elevator in the City Centre

    • Hotel
    With a stay at this apartment in Krems an der Donau, you'll be within a 5-minute walk of Wachau and Sgraffitohaus. This apartment is 1.3 mi (2.1 km) from Danube River and 0.2 mi (0.3 km) from Pfarrkirche. ...
  • Deluxe Apartment Danube-view in the Malerwinkel of D Rnstein

    • 2 Guests · 2Bedrooms
    With a stay at this apartment in Durnstein, you'll be just steps from Wachau and Danube River. This apartment is 0.1 mi (0.1 km) from Stifskirche and 0.3 mi (0.5 km) from Burgruine.
    Make yourself ...
  • Deluxe Studio With King Size bed and Parking in Krems City

    • Hotel
    With a stay at this apartment in Krems an der Donau, you'll be a 1-minute walk from Wachau and 8 minutes by foot from Sgraffitohaus. This apartment is 0.7 mi (1.1 km) from Danube River and 0.5 mi (0.8 ...
  • Deluxe Apartment With Spacious Living Room and King Bed Near DPU

    • 4 Guests · 2Bedrooms
    With a stay at this apartment in Mautern an der Donau, you'll be a 1-minute walk from Wachau and 6 minutes by foot from Danube River. This apartment is 1.3 mi (2.2 km) from Kunst Halle Krems and 1.4 mi ...
  • Deluxe Apartment in the historic centre of Krems with private parking, air conditioning and view

    • 4 Guests · 1Bedroom
    10 Exceptional (1)
    Located in Krems an der Donau, this apartment is in the city center. Karikaturmuseum and Kunst Halle Krems are cultural highlights, and some of the area's activities can be experienced at Winzer Krems ...
  • Deluxe Apartment “Art Collection" with King Bed and Air Conditioning

    • 4 Guests · 2Bedrooms
    10 Exceptional (1)
    Located in Krems an der Donau, this apartment is in the city center. Kloster UND and Donauwarte are local landmarks, and the area's natural beauty can be seen at Wachau and Danube River. Beethovenhaus ...
  • Baumhaus

    • 4 Guests · 1Bedroom
    9.8 Exceptional (9)
    Featuring mountain views, Baumhaus provides accommodation with a balcony and a kettle, around 44 km from Melk Abbey. This holiday home features a garden, barbecue facilities, free WiFi and free private ...
  • Living inStein

    • 19 Guests · 9Bedrooms
    8.2 Fabulous (245)
    Set in Krems an der Donau, Living inStein features free WiFi and units equipped with a kitchen. A dishwasher and microwave are also featured, as well as a coffee machine. All areas are non-smoking. ...
  • Wohnzimmer

    • 6 Guests · 3Bedrooms
    9.6 Exceptional (38)
    Located in a renovated 19th-century building in the centre of Krems, this spacious studio offers free Wi-Fi, a kitchen, and a balcony overlooking the garden. It is right next to a cultural exhibition space. ...

Save on Bed & Breakfast in Krems an der Donau

Are you looking for an accommodation in Krems an der Donau and do you want to save money? Choose from 20 Bed & Breakfasts in Krems an der Donau

  • Frühstückspension Leopold Janu

    • 3 Guests · 2Bedrooms
    9 Exceptional (285)
    This family-run Frühstückspension Leopold Janu is located in the picturesque wine-growing village of Senftenberg in the Wachau region. Each room offers free WiFi, a flat-screen TV, a minibar, a safety ...
  • Weinberghof Ilkerl-Luf

    • 2 Guests · 1Bedroom
    9.5 Exceptional (42)
    In a scenic countryside location at the foot of its private vineyard in the village of Rehberg, the B&B Weinberghof Ilkerl-Luf is 2,500 metres from the centre of Krems. Free WiFi is available, and hiking ...
  • Gästehaus Krappel

    • 3 Guests · 1Bedroom
    9.4 Exceptional (59)
    Surrounded by vineyards, Gästehaus Krappel houses a wine cellar and offers guided wine tours. It has a garden with a sun terrace and pergola, while breakfast is served every morning in the breakfast room. ...
  • Weinlodge Siedler

    • 4 Guests · 2Bedrooms
    9 Exceptional (34)
    Set 37 km from Melk Abbey, Weinlodge Siedler offers accommodation with free WiFi and free private parking. Fitted with a balcony, the units feature a flat-screen TV and a private bathroom with shower and ...
  • Schmankerl und Gast

    • 10 Guests · 4Bedrooms
    Located in Rohrendorf bei Krems in the Lower Austria region, Schmankerl und Gast provides accommodation with free WiFi and free private parking. There is a fully equipped private bathroom with shower and ...
  • Gästehaus Benediktinerstift Göttweig - Bed & Breakfast Monastery

    • 21 Guests · 10Bedrooms
    The guest house belongs to the UNESCO World Heritage Site of Göttweig Benedictine Abbey with 35 benedictine monks. ...
  • Landhaus-furth8

    • 2 Guests · 1Bedroom
    Featuring a terrace, Landhaus-furth8 provides accommodation in Furth with free WiFi and garden views. The bed and breakfast, set in a building dating from 15th century, is 39 km from Melk Abbey and 10 ...
  • Winzerhof - Gästehaus Stöger

    • 20 Guests · 10Bedrooms
    9.4 Exceptional (143)
    Located in Dürnstein in the Wachau Valley, just steps away from the Danube River, Winzerhof - Gästehaus Stöger features a garden, a bicycle storage room, and bicycle rental. ...
  • Gästehaus zur weißen Rose

    • 3 Guests · 1Bedroom
    8.6 Fabulous (267)
    Surrounded by vineyards at the entrance to the Wachau Valley, Gästehaus zur weißen Rose is only 1 km away from Göttweig Abbey. It offers rooms with free WiFi, satellite TV and a safety deposit box. Buffet ...
  • Pension Zierlinger

    • 4 Guests · 2Bedrooms
    7.9 Very Good (142)
    The family-run Pension Zierlinger is located in the centre of Senftenberg in Lower Austria’s Krems Valley, only 7 km away from Krems an der Donau. There is a big outdoor pool in the hotel garden. ...
  • Gasthof Klinglhuber

    • 10 Guests · 5Bedrooms
    8.2 Fabulous (776)
    Situated directly at the Krems River, Gasthof Klinglhuber is located at the edge of Krems’ Old Town, only a 5-minute walk from the train station Free WiFi is provided throughout the property and all of ...
  • Weingut-Pension Stockingerhof

    • Hotel
    8.4 Fabulous (9)
    Featuring 3-star accommodation, Weingut-Pension Stockingerhof is set in Dürnstein, 30 km from Melk Abbey and less than 1 km from Dürnstein Castle. ...
  • Gästehaus Kleine Mühle

    • Hotel
    8.2 Fabulous (201)
    In a quiet location on the outskirts of Krems, Gästehaus Kleine Mühle is a 5-minute walk from historic district of Stein and a 20-minute walk from Danube University. The garden includes a terrace and barbecue ...
  • Schmelz

    • 3 Guests · 0Bedroom
    ...
  • Gästehaus Lurger

    • Hotel
    2 Acceptable (3)
    Gästehaus Lurger is located in Krems an der Donau. Karikaturmuseum and Kunst Halle Krems are cultural highlights, and some of the area's activities can be experienced at Winzer Krems and Weingut Nigl. ...
  • Pension Altes Rathaus

    • 6 Guests · 3Bedrooms
    9.2 Exceptional (7)
    Set in Dürnstein and with Melk Abbey reachable within 30 km, Pension Altes Rathaus offers a garden, non-smoking rooms, free WiFi throughout the property and a terrace. ...
  • Asbacher Klosterkeller

    • 30 Guests · 10Bedrooms
  • Frühstückspension Täuber

    • 14 Guests · 5Bedrooms
    Frühstückspension Täuber is located in Krems an der Donau, 3.7 km from Danube University Krems and 4 km from Caricature Museum Krems. The property is situated 4.1 km from Kunsthalle Krems. ...
  • Gästehaus Fischer Rohrendorf

    • 5 Guests · 2Bedrooms
    Set 42 km from Melk Abbey, Gästehaus Fischer Rohrendorf offers accommodation with a garden, a terrace and a shared kitchen for your convenience. Both WiFi and private parking are accessible at the bed ...

Farmhouse or Hotel? Choose from the best offers

Choose the accommodation tailor-made for you for your next vacation: sleep in a farmhouse or sleep in a hotel?

Hotels in Krems an der Donau, our top selection just for you

Are you looking for hotels in Krems an der Donau? Here is a selection of the best hotels in Krems an der Donau

  • Hotel Unter den Linden

    • Hotel
    9 Exceptional (881)
    Ideally situated in the heart of the city of Krems, at the entrance to the UNESCO World Heritage Site Wachau, the family-run Hotel Unter den Linden is just a few minutes’ walk away from many of the local ...
  • Richard Löwenherz

    • Hotel
    8.9 Fabulous (371)
    With a stay at Richard Löwenherz, you'll be centrally located in Durnstein, steps from Stifskirche and within a 10-minute walk of Burgruine. This 4-star hotel is 4 mi (6.4 km) from Kunst Halle Krems and ...
  • Hotel Schloss Durnstein

    • Hotel
    9.1 Exceptional (458)
    A stay at Hotel Schloss Durnstein places you in the heart of Durnstein, steps from Wachau and Stifskirche. This 5-star hotel is 0.1 mi (0.2 km) from Danube River and 0.3 mi (0.5 km) from Chorherrenstift. ...
  • Steigenberger Hotel & Spa Krems

    • Hotel
    8.3 Fabulous (1140)
    Located in Krems an der Donau, Steigenberger Hotel & Spa Krems is within a 15-minute walk of Kunst Halle Krems and Kloster UND. This 4-star hotel is 2.4 mi (3.8 km) from Donauwarte and 2.5 mi (3.9 km) ...
  • Nuhr Hotel

    • Hotel
    10 Exceptional (3)
    Set in Senftenberg, within 42 km of Melk Abbey and 22 km of Dürnstein Castle, Nuhr Hotel offers accommodation with a restaurant and free WiFi as well as free private parking for guests who drive. ...
  • arte Hotel Krems

    • Hotel
    8.3 Fabulous (663)
    With a stay at arte Hotel Krems in Krems an der Donau, you'll be just steps from Wachau and Danube University Krems. This 4-star hotel is 0.5 mi (0.8 km) from Danube River and 0.3 mi (0.4 km) from Kunst ...
  • Parkhotel Krems

    • Hotel
    7.4 Very Good (766)
    Directly at the large city park and with free WiFi access, our 3-star-hotel lies very calmly and nevertheless very central. So you are directly in some minutes in the historical old part of town and/or ...
  • Klinglhuber Suites

    • Hotel
    9.2 Exceptional (55)
    Situated in the centre of Krems an der Donau, Klinglhuber's Suiten offer accommodation with an outdoor pool and free WiFi throughout the property. Free private parking is available on site. ...
  • Hotel Klinglhuber

    • Hotel
    8.5 Fabulous (649)
    Family-run for 4 generations, Hotel Klinglhuber is located directly at the Krems River at the entrance to the picturesque old town of Krems, only a 5-minute walk away from the train station. Free private ...
  • ad vineas Gastehaus Nikolaihof-Hotel Garni

    • Hotel
    9.5 Exceptional (258)
    Ad vineas Gästehaus Nikolaihof-Hotel Garni is a popular choice amongst travelers in Mautern, whether exploring or just passing through. Offering a variety of facilities and services, the hotel provides ...
  • Zum goldenen Engel - Fam. Ehrenreich

    • Hotel
    8.8 Fabulous (626)
    This historic, carefully renovated hotel is only a 5-minute walk away from the Old Town of Krems. It offers free Wi-Fi access and free garage parking. The history of Hotel Zum goldenen Engel dates back ...
  • Hotel Alte Post Krems

    • Hotel
    7.7 Very Good (191)
    Located in Krems an der Donau, Hotel Alte Post Krems is 1,000 yards from Caricature Museum Krems. Built in 14th century, this hotel is within 900 yards of Kunsthalle Krems and Danube University Krems. ...
  • Living inStyle

    • Hotel
    8.2 Fabulous (2)
    Situated in Krems an der Donau, 36 km from Melk Abbey, Living inStyle features views of the city. The property is around 7.1 km from Dürnstein Castle, 23 km from Herzogenburg Monastery and 41 km from Ottenstein ...
  • MALAT Weingut und Hotel

    • Hotel
    9.6 Exceptional (146)
    MALAT Weingut und Hotel is conveniently located in the popular Furth bei Gottweig area. The hotel offers a high standard of service and amenities to suit the individual needs of all travelers. Free Wi-Fi ...
  • Kolping Campus Krems

    • Hotel
    8.1 Fabulous (784)
    Surrounded by vineyards, this modern student residence is located directly on the campus of the Danube University and the University of Applied Sciences, a 15-minute walk from the Old Town of Krems. Free ...
  • Orange Wings Krems

    • Hotel
    7.3 Very Good (1095)
    This low-priced, modern hotel is located in the eastern part of Krems, 3500 metres from the centre and 500 metres from the Danube River Cycling Trail. ...
  • Gasthof Hotel Zur goldenen Krone

    • Hotel
    8 Fabulous (65)
    Hotel Zur goldenen Krone is located at the foot of Göttweig Abbey at the entrance to the Wachau Valley. WLAN access and parking are available free of charge. ...
  • Radfahrerherberge Krems

    • Hotel
    Set in Krems an der Donau and with Melk Abbey reachable within 36 km, Radfahrerherberge Krems offers a tour desk, non-smoking rooms, a garden, free WiFi throughout the property and a shared lounge. ...
  • Junior Suite With air Conditioning and Private Parking in the Historic City Centre With View

    • Hotel
    10 Exceptional (3)
    With a stay at Junior Suite With air Conditioning and Private Parking in the Historic City Centre With View in Krems an der Donau, you'll be within a 5-minute walk of Wachau and Sgraffitohaus. This hotel ...

The best hotels with swimming pool in Krems an der Donau

Book your relaxing holiday, by choosing the best deals at hotels with swimming pools in Krems an der Donau

  • Hotel Schloss Durnstein

    • Hotel
    9.1 Exceptional (458)
    A stay at Hotel Schloss Durnstein places you in the heart of Durnstein, steps from Wachau and Stifskirche. This 5-star hotel is 0.1 mi (0.2 km) from Danube River and 0.3 mi (0.5 km) from Chorherrenstift. ...
  • Nuhr Medical Center

    • Hotel
    10 Exceptional (3)
    Located in Senftenberg, Nuhr Medical Center is a 4-minute drive from Weingut Nigl and 5 minutes from Kuenringer Castle. This spa hotel is 9.7 mi (15.7 km) from Danube River and 3.7 mi (6 km) from Wachau. ...
  • ad vineas Gastehaus Nikolaihof-Hotel Garni

    • Hotel
    9.5 Exceptional (258)
    Ad vineas Gästehaus Nikolaihof-Hotel Garni is a popular choice amongst travelers in Mautern, whether exploring or just passing through. Offering a variety of facilities and services, the hotel provides ...
  • Weinresidenz Sonnleitner - ADULTS ONLY

    • Hotel
    9.3 Exceptional (155)
    Weinresidenz Sonnleitner is a popular choice amongst travelers in Furth bei Gottweig, whether exploring or just passing through. The property features a wide range of facilities to make your stay a pleasant ...
  • Hotel Alte Post Krems

    • Hotel
    7.7 Very Good (191)
    Located in Krems an der Donau, Hotel Alte Post Krems is 1,000 yards from Caricature Museum Krems. Built in 14th century, this hotel is within 900 yards of Kunsthalle Krems and Danube University Krems. ...
  • Zum goldenen Engel - Fam. Ehrenreich

    • Hotel
    8.8 Fabulous (626)
    This historic, carefully renovated hotel is only a 5-minute walk away from the Old Town of Krems. It offers free Wi-Fi access and free garage parking. The history of Hotel Zum goldenen Engel dates back ...
  • Hotel Unter den Linden

    • Hotel
    9 Exceptional (881)
    Ideally situated in the heart of the city of Krems, at the entrance to the UNESCO World Heritage Site Wachau, the family-run Hotel Unter den Linden is just a few minutes’ walk away from many of the local ...
  • Klinglhuber Suites

    • Hotel
    9.2 Exceptional (55)
    Situated in the centre of Krems an der Donau, Klinglhuber's Suiten offer accommodation with an outdoor pool and free WiFi throughout the property. Free private parking is available on site. ...
  • Deluxe Apartment Sonnleitner - ADULTS ONLY

    • Hotel
    9.5 Exceptional (38)
    Surrounded by vineyards, the modern and stylish Deluxe Apartment Sonnleitner can be found 2 km from the Göttweig Abbey and 4 km south of Krems and offers private saunas, free WiFi and iPod docking stations. ...
  • Kolping Campus Krems

    • Hotel
    8.1 Fabulous (784)
    Surrounded by vineyards, this modern student residence is located directly on the campus of the Danube University and the University of Applied Sciences, a 15-minute walk from the Old Town of Krems. Free ...
  • MALAT Weingut und Hotel

    • Hotel
    9.6 Exceptional (146)
    MALAT Weingut und Hotel is conveniently located in the popular Furth bei Gottweig area. The hotel offers a high standard of service and amenities to suit the individual needs of all travelers. Free Wi-Fi ...
  • Hotel Klinglhuber

    • Hotel
    8.5 Fabulous (649)
    Family-run for 4 generations, Hotel Klinglhuber is located directly at the Krems River at the entrance to the picturesque old town of Krems, only a 5-minute walk away from the train station. Free private ...
  • Orange Wings Krems

    • Hotel
    7.3 Very Good (1095)
    This low-priced, modern hotel is located in the eastern part of Krems, 3500 metres from the centre and 500 metres from the Danube River Cycling Trail. ...
  • Gasthof Hotel Zur goldenen Krone

    • Hotel
    8 Fabulous (65)
    Hotel Zur goldenen Krone is located at the foot of Göttweig Abbey at the entrance to the Wachau Valley. WLAN access and parking are available free of charge. ...
  • arte Hotel Krems

    • Hotel
    8.3 Fabulous (663)
    The new arte Hotel Krems is located, as its name implies, in the arts district of this beautiful town on the Danube, directly opposite the campus of the Danube University Krems. ...
  • Parkhotel Krems

    • Hotel
    7.4 Very Good (766)
    Directly at the large city park and with free WiFi access, our 3-star-hotel lies very calmly and nevertheless very central. So you are directly in some minutes in the historical old part of town and/or ...
  • Steigenberger Hotel & Spa Krems

    • Hotel
    8.3 Fabulous (1140)
    In a scenic location in the Wachau region overlooking the town of Krems, The 4-star superior Steigenberger Hotel & Spa Krems is 2 km from the centre. It offers a large spa area, and a restaurant. ...
  • Hotel Richard Löwenherz

    • Hotel
    8.9 Fabulous (371)
    With its unique location directly on the banks of the Danube, the charming, traditional Hotel Richard Löwenherz in Dürnstein is the perfect choice for those who appreciate individual service in a beautiful ...
  • Gastehaus & Weingut Aigner

    • Hotel
    Situated in Krems an der Donau, 41 km from Melk Abbey, Gastehaus & Weingut Aigner features accommodation with a seasonal outdoor swimming pool, free private parking, a garden and a terrace. ...
  • Radfahrerherberge Krems

    • Hotel
    Set in Krems an der Donau and with Melk Abbey reachable within 36 km, Radfahrerherberge Krems offers a tour desk, non-smoking rooms, a garden, free WiFi throughout the property and a shared lounge. ...

Krems an der Donau: Organize a holiday and find the best accommodation deals

According to whether you are trevellers in search of calm and tranquillity in the low season or whether you love the high season touristic destinations, in Krems an der Donau the low season period with the best offers is during the month of January, more specifically, the week from 21/01 to 28/01.
Instead, for the high season, it's possible to find more accommodation at the best price in the month of August, during the week that spans from 19/08 to 26/08.
Observing this destination at a wider spectrum, the cheapest weekend is in the month of December, from 01/12 to 03/12.
In Krems an der Donau it will be possible to find accommodation solutions at an average cost of 83 pounds per night.

Krems an der Donau and the time with the best weather for a holiday

Krems an der Donau: do you want to know which is the hottest month: the hottest month of the year is July where temperatures can reach 23°C.
If instead you are cold lovers the best month with the coldes temperatures is January, where the temperature can drop to 0°C.
On average in Krems an der Donau you will find an average temperature of 12°C.

Top Regions in Krems an der Donau