For another thing, it's got trees growing around it and inside it and on the roof; Hundertwasser called them the "tree tenants". The entire roof is a curving ramp, giving residents access to the forest on top.
And lastly, the outside of the complex is painted in colorful, sinuous stripes that resemble sedimentary layers in rock.
The building was completed in 2000, the same year Hundertwasser died.
(Image credit: Norbert Nagel)