The Beelitz sanatorium, about one hour's train ride from Berlin, is today for a large part in a state of decay. A working hospital occupies some buildings, and a few others have been renovated and now house a museum, restaurants and residential homes, but many others have been abandoned since 1994.
The Beelitz TBC sanatorium was built between 1898 and 1930. During WWI and WWII the complex was used as a military hospital (in fact, Adolf Hitler spent a few weeks there in 1916). After WWII, during which some of the buildings were heavily damaged, the Soviet army declared the whole area a military exclusion zone, and from 1945 to 1994 the complex was the largest Soviet Army military hospital outside of the USSR.
The property owners went bankrupt in 2001, and questions about further use and renovation of the dilapidating buildings - all of them officially protected as historical landmarks - are on hold. Most of the abandoned buildings are very easy to enter, and while being a popular location for photographers like myself and film makers like Roman Polanski (The Pianist) or Bryan Singer (Valkyrie, starring Tom Cruise), the already heavily damaged structures are also victims of various forms of vandalism.
In 2007 the complex was bought by an investor who so far seems serious and reliable, and the buildings are slowly being restored.
Read more about the sanatorium.