Salt mines of Soledar city in Ukraine located 300 m below the sea level can be reached by a speedy elevator. Having left the elevator, one appears to be in a huge hall the walls of which are higher than 9-storey building. In 2003 the place got into the Guinness Book of World Records as the first underground area being examined by people flying with balloons.
Welcome to Soledar!
It looks like a cell descending into a cave.