This is one of the most interesting urban building designs I've ever come across (unfortunately not in person). The hill the guy in the picture above is climbing is actually the roof of the library at the Delft University of Technology in the Netherlands (click here for their web site). The two following pictures show the same image but indifferent seasons: lounge and bask in the sun on the roof in the summer months and sled down it in the winter. The last image is a side view...and of course being a Dutch city there are a large number of bicycles lined up. Imaging if there were more urban architecture like this (it's almost Frank Lloyd Wright-ish, only with a modern green approach). I'm curious as to what the interior is like.