They’re called the “People’s palaces of Moscow” or else “Underground palaces,” and they were built during the Soviet era on the Communist idea that art and beauty should belong to the people rather than only being available in the houses of nobles.
The Great Hall, Catherine Palace, near Saint Petersburg, Russia. Note the magnificent floors inlaid with precious woods. When you enter, you are given paper slippers at the door, so the floors will not be damaged. #St.Petersburgrussia