the Lahmann- sanatorium in Dresden is to this point the most creepiest abandoned buildings i've discovered. it's located in an old part of the town inside a deep forest, so everything is very dark, plus all the windows have been shut with timber so it was quite difficult to get inside the many buldings and when you finally make it inside it's almost completely dark.
the sanatorium was found in 1887 by Dr. med. Heinrich Lahmann and soon developed into a popular santorium for the rich and famous. after WWII the russians took over the area and used it as a sanatorium for the russian troups. like many other buildings here in the east part of germany the sanatorium got abandoned after the russians left germany in 1991-1993.