Alte Donau

The Alte Donau is what remains of the Danube's old braided course through Vienna: when the river was straightened and channelled between 1870 and 1875 to stop the floods that repeatedly wrecked the city, one loop was cut off and left as standing water, and it has been a lake ever since - about one and a half square kilometres, fed by groundwater rather than the river, and clean enough that the city runs public bathing beaches on it. Sailing and rowing clubs use it, boats and pedalos are hired along the shore, and in a hard winter it freezes and people skate. The banks are lined with allotments, boathouses and restaurants, and the whole thing sits within the city with U-Bahn stations at either end, which is what makes it unusual - a proper swimming lake reachable by metro.

What you actually see

• A cut-off Danube meander - the old loop left behind by the 1870s regulation.
• Public bathing beaches - the municipal baths and free shore access.
• Sailing and rowing - the clubs and hire boats working the water.
• Boathouses and allotments - the shoreline of huts, gardens and restaurants.

When to go

May to September for swimming; winter for skating when it freezes. Half a day.

Honest expectations

Hot summer weekends fill the beaches completely. Water quality is published and occasionally drops after algal growth. The municipal baths charge; the free shore is more crowded.

Nearby

The Donauinsel and the Danube Tower are close; central Vienna is twenty minutes by U-Bahn.