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It’s difficult to compile a definitive list of the world’s biggest caves, for a few reasons. Do you measure the largest cave system by the surface area of its biggest chamber? Or the length of a single cave? Or perhaps, the overall volume of a cavern? The depth from the surface? Taking these questions into consideration, here are nine of the biggest caves on Earth.

Miao Room (China)

Open to tourists: No

The Miao Room, also known as China’s Supercave, took the title for the cave with the largest known volume measurement on Earth. The National Geographic Society funded a laser-mapping expedition to find the measurements presented at the United Kingdom’s national caving conference in 2014. The Miao Room officially measures 10.78 million cubic meters in volume and the chamber is only accessible along its underground stream.

Sarawak Chamber (Borneo)

Inside of the Sarawak Chamber
Credit: Nora Yusuf/ Shutterstock

Open to tourists: Yes

The Sarawak Chamber, located within the Mulu Caves in Borneo, was considered the largest cave by volume until the measuring of the Miao Room Chamber. The Sarawak Chamber holds the “biggest cave on Earth” title, however, since it’s still the cave with the largest measured surface area on the planet.

The Sarawak Chamber has a surface area expanse of approximately 38.3 acres and the cave’s ceiling measures higher than 260 feet. Tourists can even camp overnight inside the Sarawak Chamber if they're brave.

Deer Cave (Malaysia/Borneo)

Interior of cave with walkway leading out
Credit: ThamKC/ Shutterstock

Open to tourists: Yes

The Deer Cave (or Deer Chamber) has been called the largest cave passage on Earth and is also part of the Mulu Cave system in Borneo. Deer Cave measures roughly 2.5 miles long and stretches even farther when paired with the adjacent Lang Cave. Together, Deer Cave and Lang Cave connect to form the Deer Cave System.

Hang Sơn Đoòng (Vietnam)

Light streaming into cave from above with person standing in the light
Credit: David A Knight/ Shutterstock

Open to tourists: Yes

The Sơn Đoòng cave in Vietnam holds a top spot on a number of largest cave lists. Discovered in 1991 and explored further in 2009, the Sơn Đoòng cave measures 5.5 miles long and is said to be able to house a 40-story skyscraper within its limestone walls. A hidden jungle lies nestled 600 feet beneath the surface and is able to grow thanks to sunlight entering through an area of collapsed limestone. Oxalis Adventures offers guided tours through the Sơn Đoòng cave system.

Mammoth Cave National Park (United States)

Interior view of colorful Mammoth Cave system in Kentucky, USA
Credit: Zack Frank/ Shutterstock

Open to tourists: Yes

Mammoth Cave National Park in Kentucky encapsulates the titular cave system, which has also been called the world’s largest cave with more than 400 miles of underground terrain. But not all of the Mammoth Cave system has been explored, which is what makes the park both appealing and anxiety inducing. It’s estimated that more than 600 additional miles could exist.

Sistema Sac Actún (Mexico)

Blue/green water in Gran Cenote
Credit: Byelikova Oksana/ Shutterstock

Open to tourists: Yes

The Sistema Sac Actún in Mexico is one of the longest underwater cave systems in the world. It’s accessed through one of many cenotes (areas of collapsed limestone revealing open-air wells), but the most popular is the Gran Cenote outside of Tulum, Mexico. Cenotes are generally open to the public, but many of Sistema Sac Actún’s underwater passages are prohibited — and for good reason. Sistema Sac Actún stretches for approximately 217 miles and has an average underwater depth of over 68 feet.

Carlsbad Cavern (United States)

Brightly lit interior of the large Carlsbad Cavern National Park, USA
Credit: Galyna Andrushko/ Shutterstock

Open to tourists: Yes

Carlsbad Cavern National Park in New Mexico is home to some of the most well-known caves in the U.S. The system is comprised of more than 119 caverns and the main attraction — Carlsbad Cavern — can even be accessed by elevator from the visitors center. Carlsbad Cavern’s “Big Room” isn’t the largest on Earth, but it’s popular enough to make the list. The Big Room ranks as the fifth largest cave chamber in the country and 28th in the world.

Krubera Cave (Georgia)

Open to tourists: No

The Krubera Cave, located in Georgia, is known to be the deepest cave on Earth. It’s also the only known cave to plunge more than 6,561 feet below the surface That’s probably why casual visitors aren’t allowed. In fact, expeditions through the Krubera Cave system often involve tons of equipment and only allow caving professionals. Cavers have to traverse through tight tunnels and dive deep underwater — a feat many are too afraid to do.

Great Blue Hole (Belize)

Aerial view of iconic Great Blue Hole cave in Belize
Credit: Globe Guide Media Inc/ Shutterstock

Open to tourists: Yes

Jacques Cousteau explored the depths of the now famous Great Blue Hole off the coast of Belize in 1971 — calling it one of the best diving sites in the world. The Great Blue Hole isn’t a traditional cave, but it’s still a cave by definition. The giant underwater hole in the surface of the earth stretches for approximately 1,050 feet across and measures around 400 feet deep. The Great Blue Hole is a UNESCO World Heritage Site and is part of the Belize Barrier Reef System, which means it can be enjoyed responsibly by divers.