You’ll find no trees in the Crystal Cave (Generals Hwy., three miles south of the General Sherman Tree). Instead, you’ll find immense underground rooms filled with incredible natural calcite formations and shining polished marble. This is the underside of the parks—perhaps the most impressive (and one of only two publicly accessible) of the over 250 marble caverns within the park and national forest boundaries.

The regular tour lasts 45 minutes and takes visitors through walkable, well-lit tunnels and into grand chambers filled with curtains, stalactites, and other weird and beautiful calcite creations. A longer two-hour tour takes you deeper into the caverns, and gives you a much more detailed lesson on the cave’s history and geology.

Best of all, serious spelunkers can sign up for the Wild Cave Tour, a four- to six-hour crawl off the lit tourist trails in Crystal Cave. With a limit of six people per party, you’ll get the most serious caving experience available anywhere in Sequoia and Kings Canyon National Parks.

You can’t buy a ticket for a tour at the entrance to Crystal Cave. You’ll need to stop at either the Foothills or the Lodgepole visitors center to purchase your tickets. Then proceed on to the cave parking lot, which can take over an hour from either visitor center.

No trailers or RVs over 22 feet are allowed on the road. Be aware that even in the fall, tours fill up quickly so if possible get tickets early in the morning or even a day in advance.