Donauinselfest (Danube Island Festival) — Vienna

Held every June on Vienna's Danube Island, the Donauinselfest is one of Europe's largest free open-air music festivals, attracting over 3 million visitors across three days. Multiple stages host rock, pop, folk, electronic, and Austrian music acts simultaneously. The festival is entirely free, family-friendly, and set against the backdrop of the river and the Vienna skyline — a uniquely democratic and beloved Viennese institution.