The Donauinsel (Danube Island), an island of about 20 km in the river Danube, is known to most visitors to Vienna, Austria as a recreational mecca with bars, restaurants and nightclubs, a wealth of sports opportunities from rollerblading, cycling and swimming to canoeing and a beach that looks and feels so good that it has been nicknamed the "Copa Cagrana/Copa Kagrana" (as it lies in the 22nd District of Vienna named Kagran). For over 20 years at the end of June a couple million people (in 2005, it was 3 million) gather at the Donauinsel to visit the biggest open air festival in Europe, the Donauinselfest. The festival, which charges no admission fee, is very popular among the Viennese population and beyond.

Text Source: Wikipedia