in 19th century the danube in vienna was not a river but a conglomerate of many different riverbranches. it was only regulated in 1849. one big branch was cut and is now a standing water body: the old danube. you can swim there for free, there is a promenade to bike and walk so you can stroll to the end of the old danube and stroll back if you want.there are also nice restaurants near the water. a very charming place, you should not miss it! it's special to have such a beautiful lake in the middle of a capital :-) http://www.alte-donau.info/ http://www.flickr.com/photos/aristide/825392491/

Alte Donau is such a nice place. I am very often running along the river side; it´s just great to see all the people walking, cycling, rowing, running, skating... there is a couple of nice restaurants as welll for those needing a rest :)

To the north of the city, away from too much traffic and crowds, you can take a nice walk, and swim if you are brave enough ;) Very bicycle friendly area too!!

rented a pedal-boat, which was pretty nice; good place for swimming, too, but pretty crowded sometimes