This is a colourful expressionist landmark is an unusual and colourful apartment house by the famous Austrian architect, Hundertwasse. It has a terraced garden, undulating painted facade and trees growing out of the building. You cannot go in as it is occupied by tenant owners but you can admire it and stare/take photos. Outside there is a fountain and mosaic/shiny pillars to see and opposite is a craft village, equally colourful with famous toilets (I have already seen his famous toilets in Kawakawa, NZ, too ) and fountains. Worth taking an hour of two out to see it and buy quite tasteful souvenirs too. It makes a nice change when you are suffering from culture overload, as can so easily happen in Vienna as there is so much history.
