When I was in highschool, east of the city where I grew up, way out on the prairie, there were abandones Titan missile silos. These were the old liquid fuel rockect from the 60's. When the MX solid fuel missiles came out, all of these old silos were de-commissioned. Some teenager with a 4x4 and a winch pulled up the hatch on the emergenceny entrance and wedged it open with a cinderblock.
Word got out to the kids, and on any given Sat. night in the summer, a bunch of us would go out there to party. I wish I had brought a camera. The powerdome that housed the generators was as big as a football field. The silo had filled with water, but I bet it was ten stories down to the water.
One time, we got caught by the MPs and got a warning. Anyway, the whole experience was absolutely amazing.
There was also the remains of a WWII internment camp out in the same area, and abandoned bunkers from when the bombing range was active.