Donauinsel

Donauinsel is a 21-kilometre artificial embankment built between 1972 and 1988 to protect Vienna from Danube flooding — a piece of hydraulic engineering that gradually became the city's most-visited recreational space. Sandy beaches, uninterrupted cycling and running paths, and kayak launch points run the full length of the island. Every June, the Donauinselfest transforms it into one of Europe's largest free open-air festivals, drawing up to three million visitors over three days across multiple stages. On ordinary summer evenings, Viennese gather here to swim, inline-skate, and picnic well past sunset. The Copa Cagrana, an informal cluster of beach bars and food stalls at the northern end, keeps the social scene going late into the night, while the quieter eastern bank along the Neue Donau offers a more contemplative mood as the light fades.

Artificial island between the Danube and the Neue Donau, 13 miles for running and cycling, nude beaches in the south, Donauinselfest in June.