During the Communist era, the communist party in Bulgaria decided to build a meeting place on top of a mountain in Buzludzha. It's a circular building, which floats a bit off of the ground. Therefore, it's nicknamed the UFO-building.
After communism fell, the people trashed the whole place and left the concrete structure to break down by the elements. It's a deserted and weird, yet very interesting place to visit!
Here are the pictures.