Kartchner Caverns State Park

Top choice in Southern Arizona

This wonderland of spires, shields, pipes, columns, soda straws and other ethereal formations has been five million years in the making, but miraculously wasn't discovered until 1974. In fact, its very location was kept secret for another 25 years in order to prepare for its opening as Kartchner Caverns State Park. Two tours are available, both about 90 minutes long and equally impressive.

The Big Room tour closes to the public around mid-April, when a colony of migrating female cave myotis bats starts arriving from Mexico to roost and give birth to pups in late June. Mom and baby bats hang out until mid-September before flying off to their wintering spot. While a bat nursery, the cave is closed to the public.

The focus at the state park is on education, so there are a number of rules – no purses, no water, no cameras, no touching the walls – to protect the delicate ecosystem. Tours often sell out far in advance, so make reservations early, online or by phone. There's a campground (with cabins) and the entrance is 9 miles south of I-10, off Hwy 90, exit 302.