On Halloween night, a few of us girls walked over to Union 3 to see the underground part of one of the palaces. We were told it was a torture chamber/holding cells. I'm not sure if this was told to us to make us scared or what. But it was pretty clear to me after a short bit that it was definitely a bomb shelter. They may have kept prisoners there as well, but if necessary, they'd be able to survive a nuclear attack.