In July we went to Tucson, Arizona for a week. One of the things we checked out was the Titan Missile Museum.
It's an underground silo for an Intercontinental Ballistic Missile (ICBM) that was decommissioned in 1982 and subsequently turned into a museum.
The first portion of the tour was above ground and included various equipment.
This is the opening of the silo. The door is permanently locked in a half-open position. The open half is covered in plexiglas. Unfortunately circumstances were suboptimal for pictures.
The silo door. 760 tons of concrete and steel, running on rails.
Then we went underground where we were greeted with these friendly warning signs...