The only cave I really know of is in Crystal City next to Festus, MO. I don't know how far south the Metrolink goes but there is a very popular cave called Crystal City Underground. Quite a place to visit and stay cool. I bought a groupon for this adventure. We lived in Festus for 1.5yrs and were looking for things to do. You cross a neat old bridge and go through a tunnel to get there. The boat ride through the cave was fun! Quite a different experience from the norm. Take a sweater if you tend to get chilly. We explored outside afterwards and enjoyed that too.There is a pontoon boat ride and Don Marsan's Kayak tours are still going! This is a true treasure unlike any you have seen. Calm paddling, cool all year, dark, and one of the best guides I have ever known! No experience, too old, can't swim? No worries. Easy gliding, very stable, no stress. Relax and explore and most of all,have fun! This cave is huge over 200 acres. It's 45 min. from downtown STL. Worth a look up.