If you feel you've had your fill of redwood forests, California coastlines, and Swedish mountaintops, the earth's underground is your answer. Yes, you read that right. While not nearly as accessible as some of the ‘above ground’ wonders of the world, there are plenty of places beneath the surface of our planet that can be equally (if not more) spectacular — and far less traveled. From winding underground rivers to enormous sprawling caves, we've made a list of the ten underground wonders of the world that you simply cannot miss.

Reed Flute Cave, China

Nestled in the mountains outside the Chinese city of Guilin, the Reed Flute Cave is a spectacular cavern system that is an absolute must see. The cave is named after reeds that grow abundantly outside the cave entrance, which people have historically used to make flutes. Created by water erosion over 180 million years, this cave is covered with gorgeous stone formations that are made even more spectacular by the colored lighting that decorates the cave. It is within Chinese tradition to give the formations legendary names, like Crystal Pagoda, Fruit Forest, or Flower. Getting to the Reed Flute Cave is easy — just take bus number 3 or 213 out of Guilin and get off at Reed Flute Station. The caves aren’t open during the summer months, but that shouldn’t keep you from traveling to this spectacular wonder come fall.

Son Doong Cave, Vietnam

Deep in the heart of the Phong Nha Ke Bang National Park in Vietnam, the Son Dong Cave system is one of the least traveled places in the world. For a little perspective, fewer people have seen the inside of these caves than have stood on the summit of mount Everest. The reason? It was discovered in 2009 by the British Cave Research and Association, and was only just opened to the public in 2013. Also access to the caves is difficult, but once you're inside, you'll feel a lot like you've stepped onto an entirely different planet. The largest cavern of the system is so large you could park a Boeing 747 airplane in it, and parts of the surrounding jungle reach down into the caves creating a contrast that you have to see to believe. 

Skocjan Caves, Slovenia

Ranked as the most important caves in the world, the Skocjan Caves in Slovenia are on UNESCO’s list of natural and cultural world heritage sites. Throughout history, people have been drawn to the gorge where the Reka River vanishes beneath the earth into the complex cave system. Also situated just above the cave’s entrance is the village of Skocjan, after which the Caves are named. There are a variety of ways to see these beautiful caverns, and whether you choose to take a guided tour or venture in by yourself you won’t be disappointed. That said, we do recommend you check out the Following the Reka River Underground Tour — it follows the length of the Reka river from the cave entrance to the subterranean Dead Lake. 

Magma Chamber Thrihnukagigur Volcano, Iceland

Nestled in a dormant volcano in Iceland, the magma chambers of Thrihnukagigur (yes, it’s a mouthful) are an underground wonder definitely worth exploring. Having last erupted 4,000 years ago, there are no indications that it will be erupt again any time soon, making it completely safe to take a guide-operated elevator into the heart of the cavern. In terms of size, this chamber is exceptionally large — big enough to fit the entire Statue of Liberty. Some would say that entering the heart of Thrihnukagigur is like entering the heart of the Earth itself, but we'll let you make that call when you see it.

Turda Salt Mines, Romania

Known as one of the oldest salt mines in the entire world, Romania's Salina Turda is a deep cave that's had a variety of uses from cheese center to WWII bomb shelter. Today, it's been transformed into an incredible underground theme park all set atop a beautiful underground lake. When visiting, travelers will be sent 400 feet below the earth's surface where they will then find a bowling alley, amphitheater, and even a Ferris wheel. Trust us when we say there's nothing else quite like it.

Cave of the Crystals, Mexico

Buried beneath Nacia, Chihuahua, Mexico lies the Cave of Crystals. This former magma chamber was only recently discovered in 2000, and houses some of the largest natural crystals ever recorded. To give you an idea, the main chamber has pale white crystals rising nearly 36 feet high. While a majority of the cave system remains unexplored because of the intense heat that still radiates off the magma beneath the cavern, travelers can visit these spectacular crystals with prior approval. Even if you see only part of it all, the Cave of Crystals is well worth the extra effort needed to get down there.

Puerto Princesa Underground River, Philippines

Deep underground the island of Palawan lies the spectacular Puerto Princesa River. This subterranean river is one of the largest in the world, and was recently named by UNESCO as a World Heritage Site as well as one of the ‘New 7 Wonders of Nature’. Getting to Puerto Princesa starts at the small village of Sabang, where you can purchase a guide to lead you into the heart of these caverns. You’ll need a permit prior to booking the trip, and it’s best to book a few days in advance as there's a limited capacity. Once you have all that organized, you'll take a 20-minute boat ride across the sea to the mouth of the river, which flows deep into stunning limestone caverns. Spectacular underground waterfalls, limestone walls peppered with brilliant crystals, and 20 million-year-old fossils await. 

Waitomo Glowworm Caves, New Zealand

World renown, the Waitomo Glowworm Caves in New Zealand are exactly what you think them to be: a long water-eroded cave system filled with naturally glowing worms. Thousands of these bioluminescent creatures guide travelers on boats through a starry underground wonderland to the legendary Glowworm Grotto. The caves are cut by the Waitomo River which runs deep underground and adds to the name. Located on New Zealand’s North Island, the caves are easy to find with it’s spectacular wood crafted visitors center, and there are frequent guided boat tours that you can embark on. If you decide to travel to this natural marvel, prepare to be stunned by the living lights.

The Catacombs, Paris

Located beneath the streets of Paris, the Catacombs are one of the most visited underground wonders of the world. An intricate network of more than 200 miles of tunnels, the 13th century pathways were used in the 17th century as a solution for the overflowing city cemeteries. The result? The pathways are often lined with skulls and bones. Today, the Catacombs see lots of living people from all over the world, and serve as an interesting, educational, and eerily amazing sight. The entrance to the Catacombs is located in Paris’ 14th arrodissement at 1, avenue du Colonel Henri Rol-Tanguy. While only about a mile is open to the public, it is definitely still worthy of a descent.

Want to explore underground rivers the right way? Grab a glass kayak!