We have one cave system here where they do tours through. It's an old mining cave with streams running through it and all the trout that live in the stream there are blind. There's also a spot where the rock drops away and you're standing on a grid of rebar above water that's at least 250ft deep. They haven't been able to get anything else down there though to tell if they simply hit a rock bump out or the bottom. Its big enough for people to fit between the cave walls up to 40ft deep though.

Inside the caves is one of the few places on earth where there's natural total darkness. They said that humans would go blind in approx 3 months in there. And I always get scared over that pool lol. I've been several times, but the last time I went was around 10 yrs ago when the bat population was up, but I never forget the pool. She was telling us about how it was thought to lead out to channels to the ocean and that they had seen water snakes swim up under the bars before. They lit it up part of the way down with underwater lights, but it just makes it feel even deeper X3