There is one in Florida that is full of water to the top. Exploration shows it funnels down, then opens out into a wide cave.
Once the water level was way low, and any animal or man who fell in was permanently there. Exploration found a large turtle that some MAN cooked and ate while trapped there.
The Natural Trap Cave in WY makes me wonder how many big voids exist under the mountains that have no connecting shaft to the outside. Generally I think of the ground under me here in the Rockies as solid rock. But it obviously isn't entirely solid.