For nature lovers like me, time outside is a necessity. Communing with the natural world soothes our souls and provides a respite from everyday stresses. But what do we do when the weather’s nasty, the snow is deep, and walking outside isn’t an option?

Go underground, of course! While caving is popular in summer, winter is also a great time to explore the stunning and sometimes surreal beauty that lies just beneath our feet. Cavern tour groups are often smaller in winter, and even if the weather outside is awful, you’ll be sheltered from the elements in an environment with a constant temperature, usually in the mid-50s, while surrounded by some of the world’s most beautiful natural wonders.

Luckily, Appalachia is graced with countless cave systems, ranging from the longest in the world to one boasting a stalactite organ. (Yes, it’s a real thing.) Here are a few favorites to get you started on your spelunking adventures. 

Near Park City, Kentucky

Mammoth Cave National Park is not only the longest cave system in the world, but the park itself has been declared a UNESCO World Heritage Site and International Biosphere Reserve because of the variety of plant and animal life it contains. Tour tickets usually sell out weeks in advance during the summer months, so winter is a great time to visit this limestone labyrinth, which includes more than 425 miles of explored passageways. A range of daily tours are offered, but you might also want to visit this International Dark Sky Park at night. Outside the caves you’ll find some seriously impressive stargazing.

Front Royal, Virginia

This 60-million-year-old cave is one of the few places in the world that holds anthodite formations, which feature needle-like crystals that defy gravity by spreading in all directions. Skyline Caverns is also home to three underground streams and a 37-foot rainbow-lit waterfall, which manages to be both kitschy and stunning at the same time.

Near Lewisburg, West Virginia

At Lost World Caverns, visitors can wander through stalactites and stalagmites on a 45-minute, self-guided tour, or they can opt for the more adventurous Wild Cave Tour to explore undeveloped parts of the cavern. Discovered in 1942, Lost World includes the Snowy Chandelier, a 30-ton compound stalactite, and a beautiful column of sparkling white calcite known as the Bridal Veil. An adjacent natural history museum is chock-full of info about area dinosaurs and a prehistoric cave bear whose remains were discovered in 1967 within the cavern. Lost World Caverns is open on weekends during January-February, then returns to daily tours in March.

Near McMinnville, Tennessee

The longest show cave in Tennessee, Cumberland Caverns offers visitors a range of experiences. Walking tours can focus on history, science, or cavern legends. Adventure tours are geared toward thrill seekers who are ready to scale underground canyons. Overnight packages give you the rare opportunity to sleep underground. Discovered in 1810, this National Natural Landmark is open year-round, seven days a week.

Near Huntingdon, Pennsylvania

Lincoln Caverns thinks about its caves in a holistic way. “One thing our team does very well is educate people about caves and the underground environment, and how the outside world and the underground world tie together,” said Patricia “Ann” Dunlavy, president/general manager. Lincoln Caverns is also a good first-time cave for kids, because it offers special events including T-Rex Tuesdays, when kids can pan for fossils, Baturday Saturdays, when they can learn about bats, and blacklight tours one evening a week.

Luray, Virginia

Luray Caverns claims to be the most visited cavern in the U.S., and it’s thanks largely to a feature found nowhere else. “Visitors will hear the haunting sounds of the world’s only Great Stalacpipe Organ,” said Director of Marketing and PR Bill Huffman, “which makes tones of concert quality from the surrounding stalactite formations that cover three and a half acres — making it the largest musical instrument in the world.” The site also includes a Car and Carriage Caravan Museum where visitors can see vehicles dating from the 1760s, and Shenandoah Heritage Village, a 19^th-century farming community, created from restored historic buildings.