It’s funny you doing that one with the Missile Silo. I’ve had an idea floating around in my head about a hapless damsel wandering into an abandoned missile silo that’s filled with mud. I hadn't yet figured out an interesting story to go with it, but the most enticing aspect of the idea to me, is the thought that the missile silo is, oh say thirty or forty in diameter ― and a hundred plus feet deep. A hundred feet plus of nothing but thick mud

And I liked that one with Pippa too!