Why limit your adventures to the ground above? Spelunking lets you see the other side of the world, quite literally. Head deep underground to see spectacular stalagmites, cathedral-sized caverns, and eerie glowing creatures. The subterranean world is daunting, and at times spooky, so spelunking is not for the faint of heart. Cavers don safety gear and harnesses and descend into the ground before traversing the network of tunnels, caverns, and caves. Test your metal and get a fresh perspective on the planet.

01Thrihnukagigur Volcanic Cave, Iceland

Thrihnukagigur Volcanic Chamber Anne_Batzelona / Getty Images

Thrihnukagigur Volcanic Cave is a vast, vibrant, and otherworldly-looking magma chamber. Head into the depths of a dormant volcano to marvel at the brightly colored and strangely shaped rock formations. Take a journey in a lift basket down 198 meters underground and watch as the rocks change and see the reds, violets, blues, yellows, and oranges that come from the heat and pressure caused by the eruption of the volcano. Thrihnukagigur last erupted four thousand years ago, so when the volcano went dormant, the magma drained away instead of sealing the chamber.

02Carlsbad Caverns, New Mexico

Carlsbad Caverns elan7t50 / Getty Images

Carlsbad Caverns is a national park with a vast network of underground caves. The 'Big Room' spans 8.2 acres, and narrow passageways lead to stunning views of the Spider Cave and the Hall of the White Giant. The Natural Entrance offers incredible views looking down from the greenery of the park into the caves. However, the trail into the caverns is steep and accessible only to accomplished hikers.

03Great Blue Hole, Belize

Great Blue Hole Belize Michael Conlin / Getty Images

Don scuba gear and dive into the Great Blue Hole in Belize to explore a vast cave world. A ring of corals surrounds the opening to the vertical cave, and the cave itself is 1,000 feet across and 412 feet deep. There was a time when the cavern was above sea level, and the stalactites and dripstone sheets from that period are still there today.

04Glenwood Caverns, Colorado, USA

Glenwood Canyon Donyanedomam / Getty Images

Glenwood Canyon is home to a gorgeous hanging lake, lush forests, and diverse wildlife. The caverns are less frequented and are not for the faint of heart. Those who are willing to crawl, wriggle, and squirm through the cramped and dark caverns will see spectacular cave formations and alien-looking stalagmites and stalactites that few have ever laid eyes on. Some of the crawl spaces are just 18 square inches in size.

04Waipu Cave, New Zealand

Waipu Cave Glow Worms MarcelStrelow / Getty Images

The Waipu Caves are karst and limestone caves with a gentle track leading up to them. The mouth of the cave features intriguing rock formations and a glowing marvel deeper down the cave. Turn off your torch, sit quietly, and look up to the cave ceiling to see glow worms in galaxy-like clusters illuminating the cave with their soft blue light.

06Luray Caverns, Virginia, USA

Luray Caverns, Virginia drashokk / Getty Images

The Luray Caverns in Virginia, U.S., is located in Shenandoah Valley. The majestic caves were formed millions of years ago, and feature cathedral-like caverns with ten-foot-high ceilings. One of the most iconic formations in the cavern is the Stalacpipe Organ, which makes musical sounds when the rocks are tapped.

07Fingal's Cave, Scotland

Fingal's Cave, Isle of Staffa Totajla / Getty Images

Fingal's Cave is a basalt cave located on the Isle of Staffa, off the shores of Scotland. This stunning cave is made up of hexagonally jointed basalt columns. The view from the outside is impressive, with the columns being so uniform they almost appear humanmade. Inside, the shape of the ceiling creates some incredible cathedral-like acoustics. Famed explorer Sir Walter Scott spoke highly of the caves, calling them one of the most extraordinary places he had ever seen.

08Meramec Caverns, Missouri, USA

Meramec Caves LindaJohnsonbaugh / Getty Images

Missouri is known as "the cave state" because it plays host to over 6,000 surveyed caves. The Meramec Caverns is a tourist-friendly destination, with rangers offering guided tours for caving novices to enjoy. The cave is home to some mineral formations with unusual shapes and bold, bright colors. The formations built up over thousands of years and combined delicate stalagmites with imposing alien-like rock formations.

09Gunung Mulu National Park, Malaysia

Gunung Mulu National Park zodebala / Getty Images

The Gunung Mulu National Park is the home of the biggest network of caves in Southeast Asia. So far, more than 186 miles of caves and passages have discovered, and international caving enthusiasts are still exploring miles of tunnels and caverns. The Sarawak Chamber, one of the best well-known spots, is the world's largest cave chamber.

10Bohol, Philippines

Hills of Bohol swissmediavision / Getty Images

The chocolate hills of Bohol, with lush greenery and abundance of mounds, are a fascinating sight when viewed from above. Explore the village on the ground, and you will find more than 1,400 caves of varying sizes. Some of the caves contain rare plants and wildlife, while others lead to underground waterways. Many of the caves were once WWII hideouts. The Hinagdanan cave, for example, was used by Filipinos, hoping to avoid detection by Japanese troops.