A municipal housing project unlike any other in Europe: Friedensreich Hundertwasser's gleefully eccentric apartment block was completed in 1985 with the explicit aim of breaking every modernist rule. Colour blocks clash, lines wobble, trees sprout from balconies and through windows, and no two windows are alike.
The interior is private (people actually live here), but the exterior and the small Hundertwasser Village across the street can be visited freely. The same architect's Kunst Haus Wien, a few minutes' walk away, displays his paintings and graphics in a similarly subversive building. Tram 1 to Hetzgasse.