Meramec Caverns in Missouri - I've been several times and still enjoy it. It's the Tom Sawyer caves, you know, from the books. There's a room where they hold balls and stuff, inside the caverns. Too cool.
Fantastic Caverns - America's Only Ride Thru Cave! ... Springfield, Missouri, U.S.A. I've been here...it was so cool to see all the stalagmites and stalagtites and hear about what the caves were used for in the past!
The karst formation of Phong Nha-Ke Bang National Park, in Viet Nam, has evolved since the Palaeozoic (some 400 million years ago) and so is the oldest major karst area in Asia. Subject to massive tectonic changes, the park’s karst landscape is extremely complex with many geomorphic features of considerable significance.
Meramec Caverns – Located a little over an hour from St. Louis in Stanton, Missouri, this cave system is now considered one of the primary attractions along former Route 66. There are billboards for miles advertising the Meramec Caverns, and they really do live up to the hype. Take a break from the Missouri heat and head underground for a guided tour through stalagmites, stalactites, and rock formations that are tens of thousands of years old.