I used to be a missile silo

And not just any missile silo, but an intercontinental ballistic missile silo.

This old ICBM silo in Albiene Texas has been decommissioned and turned into a pool for scuba diving. It was mentioned on an episode of Geo Quiz as perhaps the deepest pool on earth. (The show focuses most of its attention on the intentional pool Nemo33 in Brussels, an indoor pool 33 meters deep and 33 degrees celcius.) It's a fascinating example of adaptive reuse and demilitarization.

Listen to the MP3 Audio of the GeoQuiz.