Prison

During the Cold War, a secret prison was built in an anti-nuclear bunker. This place was used as a special prison for agents from foreign secret services. We would probably never have found out about it if it hadn't been for one CIA agent...

He managed to escape under unexplained circumstances. Due to the leak of information, the prison was considered no longer a secret place and so it was no longer used. Over time, it fell into oblivion. After the change of regime, all the land was returned back to its original owners. The owner found the prison completely untouched... No one has ever found out how the CIA agent escaped...

Can you escape before changing of the prison guards?