Tons of limestone caves in Missouri. Most of them largely unexplored/undocumented. It's generally believed that most of the caves are interconnected and you could likely navigate much of the Ozark region via the cave networks if you don't mind the probability of death in spelunking. Even the border with the plains is littered with caves, sinkholes, etc.
Perhaps after we don't have to worry about old age and secure our estates, we can go on Skyrim-esque adventures into caves to figure out if the dwemer are just a myth.