The Palace of the Parliament is the biggest civil building of the world and goes as deep into the ground as it goes up into the sky. An unimaginable network of corridors and only a few of them can be visited. The room on the photo is the Ballroom which is the biggest room of the palace.
More about this image here: https://sumfinity.com/hdr-photos/romania/bucharest/palace-of-the-parliam...
