Adventure travelers are always looking for the most exciting attractions. From mountains to dense jungles to the deep sea, there are plenty of places to find adrenaline-producing activities. Caves are one of the most underrated and overlooked types of adventure attractions. These underground worlds can house amazing rock formations and exotic animals. Some caves are equipped for tourists, but others have challenging terrain that can bring excitement to any adventure-seeker. Of course, heading off to explore a local cave is one thing, but finding the world’s largest, most-amazing caves is something completely different.

Travelers who want to explore the world’s most interesting underground attractions should add these caves to their list of must-visit destinations.

Waitomo Glowworm Cave

Photo: 4nitsirk / Flickr

This cave, in northern New Zealand, does not stand out because of its underground landscapes or mineral formations. Rather, what makes Waitomo special is its unique inhabitants. Glow-worms inhabit the inner chambers of this cave. They cling to the ceilings and walls, letting off light with their bodies. The cave also feature underground waterways, which can be traversed by boat. Because of its unique inhabitants, Waitomo is a popular tourist destination that many domestic and international visitors put on their itineraries.

Harrison’s Cave

Photo: Ben124. / Flickr

This cave, on the Caribbean island of Barbados, is a very popular tourist attraction. It is easy to reach thanks to an underground tram that takes visitors down to the most colorful chambers. The tram lets people off at certain points so that they can see the mineral formations up close The cave was formed when mineral-rich water eroded an underground deposit of limestone. The result is a collection of very unique rock and mineral formations. The highlight of Harrison’s Cave is the Great Hall, a large chamber that measures 100 feet from floor to ceiling.

Mammoth Cave

Photo: joannapoe / Flickr

This large cave network in the US state of Kentucky is the longest cave network in the entire world. Its tunnels stretch for 390 miles, and additional areas are still being discovered today. The cave is part of a national park, so some of the tunnels are well kept and there are facilities for taking long tours through the cave’s most spacious chambers. There are multiple entrance points inside the park. The National Park Service offers regular range- guided tours that pass the most impressive rock formations, chambers and underground rivers in the system. Some of the ranger-led tours are more challenging and can be as long as half-a day in length and require people to carry their own lighting.

Carlsbad Caverns

Photo: Glamour Schatz / Flickr

This is another cave system that is overseen by the US National Park Service. Located in southern New Mexico, Carlsbad is surrounded by desert landscapes. Carlsbad’s Big Room, a large, easily reachable chamber, is the second largest cave chamber in the world. Erosion by mineral rich waters has created a very impressive array of formations inside the caverns. Several of the “trails” through main areas of the cave can be used for self-guided tours (a rare option for cave visitors, who are usually only allowed into caves as part of guided tours). Ranger guided tours lead to more remote and uncrowded sections of the caverns.

Yellow Dragon Cave

Photo: SteFou! / Flickr

This cave might not be one of China’s largest, but it is one of the most easily reachable and most stunningly beautiful caves. Yellow Dragon is located in the tourist zone near West Lake in Hangzhou City (a major city near Shanghai on China’s central coast). The formations inside the cave are natural, but colored lights and some man-made elements make this an interesting attraction for casual sightseers as well as cave explorers. Stairs make it easy for people to get an up-close look at the rock formations. Because is offers easy access and has a whimsical atmosphere, Yellow Dragon Cave is a good destination even for people who aren’t interested in exploring underground.

Eisriesenwelt Cave

Photo: Franconian / Flickr

This unique ice cave is located in the alps of Austria. The name in German means World of Ice Giants. The cave has amazing ice formations that were formed by melting snows on the mountain. This cave stretches for more than 42 kilometers, making it the longest ice cave in the world. Tourists can only visit the first section of the cave, which is about a kilometer long. Fortunately, this area boasts most of the beautiful ice formations for which Eisriesenwelt is known.