Whoa, I just found out about this! What a spectacularly beautiful building! It looks like a flying saucer. This was built in 1981 and was used by the Bulgarian Communist Party for various types of gatherings including award ceremonies, educational and diplomatic events. Sadly, eight years later it was abandoned and now lies in a serious state of disrepair.
Below are some websites that contain more pictures and information about the Buzludzha Monument as it is currently known. Ignore the negativity and enjoy the pictures and historical info.