Discovered on accident by a local Chinese villager in 1992, the Longyou Grottoes are a series of underground man-made caves. There are a total of 36 caves. They were originally flooded but some are drained and open for tourists. They’re dated back at least 2,000 years. How they were constructed still remains a mystery.

The world’s longest underground navigable river, the Puerto Princesa Underground River is located in the Philippines under the island of Palawan. Over a million years ago, the river channeled its way through the caverns and caves.

The Ozarks State Park in Missouri is home to many amazing caves and caverns, thanks to a natural drainage system. The Angel Showers is a unique part of the experience, where water seems to come out of the ceiling as if from nowhere.

In the wake of the Cold War, President Eisenhower worried about running the country during a potential nuclear war. So, they build the Greenbrier Bunker for Congress in the event of an attack. Of course, it was never used and is now a beautiful relic of the past and a popular tourist attraction.

Wanting to escape his father, Baldassare Forestiere immigrated to the United States in 1901 from Sicily. He purchased 80 acres of land and started digging, creating catacombs after the ancient ones he admired back home. However, instead of them being dark and dreary, there’s plenty of light to grow trees and plants. It became the Forestiere Underground Gardens.

In Turda, Romania, lies the Turda Salt Mines. First excavated in the 17th century, it has been transformed into several things, including a cheese factory and a bunker during WWII. Now it’s an underground theme park. Along with rides, you can find mini-golf and ping pong tables.

Forgotten for 1,000 years, the Reed Flute Cave in China was discovered by Japanese refugees during World War II. Later, ink writing was found in the caves dating back to 792 CE. However, it’s the multi-colored stalagmites and stalactites that make it a true wonder to behold.

Located in Slovenia, the Škocjan Caves are exceptional for their extreme depths. They go down 656 feet (200 m), have one of the largest underground chambers, and are popular for studying the karstic phenomena.

Coober Pedy is an underground city located right in the middle of Australia, thousands of miles away from Australia’s capital city. It started in 1917 as the largest opal operation and progressed into an entire community full of apartments for the workers and their families to escape the unrelenting, scorching heat.

The Dambulla Cave Temple is at the center of Sri Lanka and is a Buddhist temple with 153 Buddhist statues as well as statues of Hindu gods and Sri Lankan kings. Many of the carvings and statues are still very well preserved, which is impressive considering it dates back to the third century BCE.

These caves were discovered in 1887 by English surveyor Fred Mace and local Maori Chief Tane Tinorau. As they navigated the dark caves they discovered that bright luminescent lights hung up on the ceiling. Those lights were glowworms, bioluminescent larvae found all over the caves. Eventually, they found a land entrance, and it’s the same used today for tourists.

The Cheyenne Mountain Bunker is the underground site for NORAD, a joint effort by the United States and Canada to defend their airspace during a nuclear attack. In the 1960’s, to protect themselves, they hollowed out the mountain and constructed a massive bunker on top of springs.

Underneath London lies the catacombs of the West Norwood Cemetery. Started in 1837, it includes 95 vaults and private and shared spaces that can hold up to 3,500 coffins. However, it has ceased being used since the 1930’s. Some coffins have been moved, but many remain

The Mayakovskaya Metro Station is Moscow’s most impressive architectural subway. Built in 1935, its gorgeous display of murals and arched walkways is a testament to Russian architecture and design. Originally built for Russian workers, it’s now open to their 9 million residents.

Poço Encantado, located in Brazil, is famous for its geological wonder known as the Enchanted Well. The pool of water in the cave hit by the sunlight creates a gorgeous and radiant sight.

Built during the Vietnam War by the Viet Cong, the Củ Chi Tunnels are extensive interconnected tunnels that stretch for tens of thousands of miles. The Viet Cong used the tunnels for their guerrilla warfare tactics, and American and South Vietnamese troops would frequently send in troops known as “tunnel rats” to investigate the tunnels.

As the longest, deepest, and most complete tomb in ancient Egypt, the Tomb of Seti I is quite the marvel. Discovered by Giovanni Battista Belzoni in 1817, the tomb was clearly a hallmark project of Seti I, with its complex structures and artwork.

The Les Catacombes de Paris is an underground labyrinth of tunnels full of skulls stacked on top of each other. They’ve been there since Roman times and are believed to stretch out for at least 200 miles. It’s believed 6 to 7 million former Parisians are buried in the catacombs. And, of course, not all areas of the catacombs are open to the public.

During World War II, Churchill, his cabinet, and the rest of their staff worked tirelessly to plan and strategize their way to victory. To do it in a safe environment, they created a bunker for their entire operation. Today, the bunker and the war rooms are a museum with many of the original items and objects of the time.

Derinkuyu Underground City is an ancient and complex underground city underneath modern-day Turkey. The tunnels are full of dwellings and homes and could house up to 20,000 people if they needed to. The city reaches around 250 feet deep (76 m). No one knows how old it is or what civilization originally built it.

Found in Chihuahua, Mexico, the Cave of Crystals is definitely a sight to behold. It has some of the largest natural crystals in the world housed in its main chamber. Unfortunately, due to the hot magma underneath the cave, it’s mostly too hot and humid to explore fully.

Believe it or not, deep within the Grand Canyon is one of the deepest, darkest, and quietest motel rooms on the planet. The motel room is built within cavern walls that are over 65 million years old. It has zero humidity and nothing lives within the cavern. It’s completely furnished with everything one might need.

Want to party underground? The Dom im Berg in Austria is a cave full of tunnels once used as air strike shelters during World War II. Today, however, it’s been converted into one of the hottest nightclubs in Europe. It can easily hold up to 1,000 people.

Built in 1788, the Edinburg Vaults were constructed to house the craftsman and labor elements of the city, allowing local tradesman to work and conduct business. It housed most of the criminal underworld as well. Each level had workshops, taverns, and living spaces. Part of the vaults, however, had a huge design flaw which allowed the upper parts of the city’s run off to drip into the vaults. It also became rife with Irish immigrants fleeing the potato famine which only increased poverty, slums, and prostitution. No one knows when the vaults were closed, but they were rediscovered in the 1980’s.

In the northern part of the Lishan Mountains is the tomb of the first emperor to unify China, Emperor Qinshihuang. It’s an incredible find. They started construction in 264 BCE, recruiting workers from all over the country, to work on the underground city and tomb which is full of terracotta warrior statues. It is the largest tomb in Chinese history.