The "top secret" T.U.F.F. Test Bunker is a testing facility and tourist attraction located in the desert, that appeared in Iron Mutt. It is home to a gift shop, a buffet, and a testing site.
The bunker has not appeared in any episode since. It is unknown if it will make another appearance.
- Perhaps jokingly, the bunker, the gift shop, and the buffet are all referred to as being top secret. The irony is, they aren't.