A rather dreamy place worth a visit is the former rehabilitation centre Beelitz Heilstätten near Berlin in Germany. It is a vast area of varied buildings being constructed in the early 20th century with a quite modern concept for healing and recovery.
After WW II it was seized by the Soviet Red Army which left Germany and this area in 1994. Nobody felt responsible for the place afterwards or had an idea for further use so nature took over control quite easily.
Some years ago the place was changed into some kind of openair museum, and a long freestanding bridge was built for viewing the amazing ruins from the very height which requires however the payment of an entrance fee.