From Caves, Tunnels And Salt Mines: The World’s Top Underground Tourist Locations

The Mulu Caves are located in the Gunung Mulu National Park in Borneo and are one of the top tourist attractions in Malaysia.

The park encompasses incredible caves and karst formations in a mountainous equatorial rainforest setting.

The Mulu Caves in Borneo are some of the most expansive on Earth. Carved out of limestone in Gunung Mulu National Park, the caves span at least 225 miles (362 kilometers) of underground passages.

The park encompasses incredible caves and karst formations in a mountainous equatorial rainforest setting.

Tours of this engineering marvel, built to keep Tokyo dry during the rainy season, take place three times a day.

Tokyo G-cans project: widely known as Tokyo underground flood tunnels is the networks of tunnels 6.4 kilometers (four miles) long built deep under the ground in the Tokyo suburbs.

Main 'cathedral'.

It looks like an underground temple or, as the English language brochure describes it, an underground Parthenon-like structure.’

All this infrastructure is dedicated to prevent flooding when Tokyo metropolitan area rivers are overfilling during the rain seasons or in case of typhoons.

You can explore this Viet Cong supply route -- if you're thin enough.

The Cu Chi Tunnels are an elaborate underground community made up of 250 km of tunnels and chambers below the city.

The tunnel systems were of great importance to the Viet Cong in their resistance to American forces, and helped achieve ultimate military success.

Things to see include statues, a chapel and a cathedral carved out by miners, all under light cast by chandeliers made from rock salt.

A chapel and cathedral carved out by miners are highlights here, under chandeliers made from rock salt.

The neatly stacked piles of bones within include the remains of many who lost their heads to the guillotine during the French Revolution.

A tour explores one mile of the 180-mile-long maze of tunnels, which lie at a depth of 20 meters.

Just a small amount of the remains of nearly 6 million people that are located in the Catacombs.

The Catacombs are one of the 14 City of Paris’ Museums that have been incorporated since January 1, 2013 in the public institution Paris Musées.

Tours pass by neat stacks of bones, including many Parisians who fell victim to the guillotine.

The Shanghai Tunnels, also known as the Forbidden City, are believed to have been used for other illegal activities such as prostitution.

The tunnels connect several basements of local hotels and bars to the Willamette River. The tunnels run from Old Town to downtown Portland.

Between 1850 and 1941, men were “shanghaied,” or kidnapped, typically through trapdoors in bars and saloons, and held in the tunnels until they were sold to sea captains as slaves. Women were also captured and sold into prostitution, often transported to other cities.

“The Shanghai Tunnels, less commonly known as the Portland Underground, are a group of passages running underneath Old Town/Chinatown down to the central downtown section of Portland, Oregon, United States.

These underground passages wind from numerous bars and hotels to the river.

This former plague-struck part of the city was long sealed up.

Back in the 1600’s, Mary King’s Close and neighbouring Closes were at the heart of Edinburgh’s busiest and most vibrant streets, open to the skies and bustling with traders selling their wares to the Old Town’s residents. Why would this street find itself underground 400 years later?

A unique and historic site, it is a dark, underground time capsule, thought by many visitors to be haunted by its former inhabitants.

When fire swept through Seattle in 1889, another city was simply built on top.

An image of the "Seattle Underground"— the facade seen here was at street level in the mid-1800s

A former bank; the vault door is in the background on the right

The concrete floor of the former meat market was originally at the level of the wooden platform on the left, but sank over time because of decomposing sawdust fill.

Carving of Cappadocia's vast underground cities may have begun three millennia ago.

Almost half of Derinkuyu is open to tourists. It's connected to another subterranean settlement you can explore, Kaymaklli, via an eight-kilometer tunnel.

Derinkuyu, extending to a depth of 60 meters, is the largest cave -- it once housed 20,000 people, as well as their livestock.

It's known early Christians hid in the man-made caves while they were still being persecuted for their religion.

Most residents of this South Australian town live underground, to escape the blazing outback heat. There are subterranean shops, a hotel and a restaurant.

The Underground Restaurant in Coober Pedy. Most establishments are underground as temperatures above ground can reach over 50 degrees in summer.