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Photo: Daniel-tbs, CC BY-SA 4.0 via Wikimedia Commons
The Gänsehäufel is the biggest open air beach in Vienna, and is operated by the city. You can lie on the grass, swim in the Old Danube or swimming pools including a wave basin and a water slide. There are several other activities available like rope climbing, stand up paddling and miniature golf, but don't expect the level of an upscale waterpark. There is a large nudist section available, too. Besides leisurely activities, the whole bath is noteable for its well-preserved functionalist 1950s buildings.
© OpenStreetMap contributors
One of the bigger social housing projects of the "Red Vienna", the Goethehof was built 1928-1930 as living blocks (~700 apartments) surrounding a courtyard. The architectural style is modern-functionalist with some art déco-elements. As all of the housing projects of the social democratic Vienna (1919-1933), it was a quantum leap in housing quality for the working class. During the Austrian Civil War (1934) it was one of the strongholds of the resistance against Austro-fascism and even suffered the one and only air-raid during this conflict.
Danube Island
This island was built for flood protection and separates the artificial Neue Donau (New Danube) canal from the Donau (Danube). It offers many opportunities for outdoor activities, including canoeing, waterskiing, cycling, and swimming. There are a number of free beaches on the northern and southern ends of the island, and toward the center are a number of restaurants, bars, and nightclubs.
Donaucity-Kirche
A modern Catholic church designed by the internationally-renowned Austrian architect Heinz Tesar.
Vienna International Centre
This complex was completed in 1979, and is the seat for such international agencies as the IAEO, UNHCR, UNOV, and UNODC. General tours are offered for the public, as well as tours for those interested in human rights or arts.
Tallest building of Austria, with an "observation deck" at 207 m.
This is one of the biggest climbing gym in Vienna with 1200 mm² lead walls and 400 m² boulder walls. It is operated by the Viennese Naturfreunde. It hosted several IFSC Boulder Worldcups.