It's the oldest tourist trap on Route 66, and if you miss one of its umpteen trillion billboards along highways north, south, east and west, then you shouldn't be behind the wheel of a car. Meramec Caverns is an in-ground labyrinth of mineral deposits and caves that trail off into unique formations and rooms. But the best part for us wimps who hate the Missouri heat is its year-round temperature: 62 degrees. Nature must have done this on purpose, as a necessary respite from the summer steam. Perhaps that's why, underneath the St. Louis region, a network of subterranean caves crawls through the earth -- Mother Nature's way of keeping us cool?