Ten places we think are worth the trip, hand-picked, not an exhaustive list, just a place to start.
One of the most famous cave systems in the world
Largest cavern system in the eastern US
Tallest underground waterfall in the US open to the public
Famous roadside attraction with a long promotional history
One of the longest cave systems in the world
Third-longest cave in the world
Largest underground lake in the US (Guinness record)
Historic Colorado cave attraction
Only mainland sea lion rookery in the continental US
Largest known commercial cavern in Texas