California is honeycombed with caves, from the volcanic landscape of the far north to the deserts of the south.

Some have been modified for tourism, with electricity that illuminates crystaline formations on their walls and ceilings. Others are au natural, tailor-made for a dark, daring adventure into Earth. Choose the cavern that suits you best and don't forget your flashlight!

Lava Beds National Monument

(Courtesy of @lavabedsnps)

At Lava Beds National Monument in California’s far northeastern reaches, you can choose your own adventure from among the park’s 18 large caverns. The least challenging caves are family-friendly, relatively short, and include Lava Beds’ only developed options—Sentinel, Mushpot, and Merrill. But if you’re up for a challenge, skip the "moderate” caves and head straight for those marked with a black diamond. Protective helmets, knee pads, and gloves are a must for these explorations, and they recommend purchasing a map because there’s a real risk of getting lost inside. The longest of them all is Catacombs Cave, a nearly 7,000-foot-long cavern with a ceiling that rarely exceeds three feet in height.

// 1 Indian Well (Tulelake), nps.gov/labe

Black Chasm Cavern

(Courtesy of @fishologistbear)

It’s true that some of the mystique of Black Chasm Cavern was lost when developers added flights of stairs, walkways, and spotlights to facilitate the tourist experience, but not even these man-made accommodations can mar the majesty of this cave in Amador County. It’s especially known for its abundance of helictites, spindly, directionally challenged speleothems found in just five percent of the caves on Earth. The vertical chambers also contain a beautiful blue lake at their heart. Fifty-minute tours are $19 for adults 13 and up, and $11 for ages five to 12.

// 15701 Pioneer Volcano Rd (Volcano), cavetouring.com

Arroyo Tapiado Mud Caves

(Courtesy of @andrewclimbsrocks)

Caves in California—hell, caves pretty much anywhere in the world—are typically formed in limestone karst or lava landscapes. But at Anza-Borrego Desert State Park in Southern California, they’re born of mud. In fact, the caverns here make up the most extensive mud cave system in the world; no one even knows how far they extend into the earth. The only way to reach them is on an eight-mile dirt road where only 4x4s go. Be careful once you arrive: Portions of the fragile cave system can collapse after it rains.

// 200 Palm Canyon Dr (Borrego Springs), parks.ca.gov

Bear Gulch + Balconies Caves

(Courtesy of @a.study.in.charlotte)

There are two caves to investigate at Pinnacles National Park: Bear Gulch and Balconies. Both are talus caves, which have a haphazard construction formed by falling boulders lodging into crevices in the rock. Both caverns can typically be seen most of the year (though check for temporary closures before you make the trek), but the lower section of Bear Gulch Cave, which is broken into two passages, is only open around March and April. The rest of the year, it’s closed to protect the endangered Townsend’s big-eared bats hibernating inside. While neither cavern is especially long, both can only be reached on a hiking adventure via the trails that bear their names.

// 5000 East Entrance Rd (Paicines), nps.gov/pinn

Mercer Caverns

(Courtesy of @ashannon95)

Mercer Cavern has been developed for tourism with the requisite viewing platforms, stairs, and electricity. But this cave outside of Murphys is still as fascinating as it was in 1885 when first discovered by Euro-Americans. The cavern has thousands of textbook-perfect speleothems, including spiked orange dogtooth spar crystals, twisting helictites, rootsicles that span from ceiling to floor, and delicate aragonite crystals. Forty-five minute tours are $20 for adults, $13 for ages three to 12.

// 1665 Sheep Ranch Rd (Murphys), mercercaverns.net