Nestled between national parks, big cities and places you may have considered “the middle of nowhere” are hidden gem outdoor spaces. While some of the world’s most famous caves can be found in Greece, Italy and New Zealand, some are in the United States offer otherworldly experiences.

Pack your best hiking shoes and dry bags. These are the best seven caves worth visiting in the United States.

Mammoth Cave National Park

People travel from all around the world to witness Mammoth Cave up close. It has the world’s largest network of natural caves and underground passageways, which are characteristic examples of limestone formations.

There are at least 285 miles of surveyed passageways within the property and another 80 miles outside the property. Scientists and researchers say the park illustrates a number of stages of the Earth’s evolutionary history. The flora and fauna is one of the richest wildlife with more than 130 species.

Its unique history and rich diversity of plant and animal life are why the park earned a UNESCO World Heritage Site and International Biosphere Reserve title.

Ruby Falls Caves

Ruby Falls is located within Lookout Mountain in Chattanooga, Tennessee. Discovered in 1928, Ruby Falls is home to the tallest and deepest public underground waterfall in the United States.

The underground waterfall is located more than 1,120 feet beneath the mountain’s surface.

Visitors will descend about 26 stories into the cavern in the mountain before exploring the scenic path of the waterfall with a tour guide.

Carlsbad Caverns

Carlsbad Caverns National Park is located in the Chihuahuan Desert of southern New Mexico. It’s the largest desert in North America as it extends from south of Albuquerque and the Mexican states of Chihuahua, Coahuila, Durango, Nuevo León and more.

Underneath this national park are more than 300 caves beneath the park’s surface.

At least 113 formed when sulfuric acid dissolved the surrounding limestone. Lechuguilla Cave is the nation’s deepest and fourth longest limestone cave at 1,567 feet.

Lava Beds National Monument

Another national park travelers can experience caves at Lava Beds in Tulelake, California. Volcanic eruptions on Medicine Lake created a rugged landscape with more than 800 caves throughout the park.

Before entering the lava caves, visitors need a permit. Cave permits are free, but it helps to ensure visitors are ready to enter the caves safely. There are 24 caves people can explore, and each is different. Park-goers can choose between the least, moderately, and most challenging.

Luray Caverns

Luray Caverns are deep beneath Virginia’s Blue Ridge Mountains. This beautiful natural landmark is where visitors will find the largest caverns in the eastern portion of the United States.

Visiting the caves is a surreal experience. The caverns feature a group of chambers that range from 30 feet to 140 feet in height. The chambers are filled with towering stone columns and crystal-clear pools. Adventures can explore the caves because of the connected corridors, stairways and bridges illuminated by indirect lighting.

Cosmic Cavern

Located in the town of Berryville is one of Arkansas’ most beautiful natural attractions: the Cosmic Cavern. It’s the state’s largest privately owned “show cave.”

It features a 9-foot soda straw, the longest known in the Ozarks, and two bottomless cave lakes.

There are two ways to explore Cosmic Cavern. The first way is through a guided walking tour that takes less than two hours. The guide will highlight the many inside formations, including stalactites, stalagmites, flowstones, soda straws, helictites, cave bacon, draperies and other speleothems.

A wild tour is the second option. Guides will take adventure enthusiasts to places rarely experienced by tourists during regular business hours. Guests will see stunning sights, explore bottomless lakes and crawl through the limitless depths of this beautiful cave.

The Lost Sea Caverns Tennessee

The Lost Sea is a unique natural wonder known as the largest underground lake in America.

A guide will take visitors on a journey of explaining the cave’s history and interesting facts. At the bottom of the cave is where the boat ride on The Lost Sea begins. The lake covers more than four acres and is recognized by the U.S. Department of the Interior as a Registered National Natural Landmark, due to its extensive collection of rare “cave flowers.”

The lake is located 140 feet below the ground level.