On the surface, there are plenty of amazing things to see on Earth, but it truly is only half the story when it comes to some other amazing things to see, as people don’t generally think to look down, or rather, under the Earth to find some hidden treasures. Underground there is plenty of ancient ruins, tunnels, naturally occurring phenomenon, and amazing man-made structures to see and experience if a tourist just knows where to look. It can be a creepy thing to think that above your head is the crust of the Earth and that at any moment it could come down, but most of these places are very stable and served a greater purpose at some point in life.

Looking through this list, there are many reasons why underground just became a good place to build or to find some pretty incredible things. For starters, it was great for hiding, and was tough to locate, making it a great place for a secret hideout. But check for yourself and see some incredible discoveries and places to visit under your feet, and think when traveling to look down, just as much as looking up. There might be something to find or see by doing so.

25 Turda salt mine, Romania

Not all mining produces gold and diamonds, as there is big business in mining for salt. The Turda salt mine is one of the largest in Romania until mining stopped in 1932.

According to CNN, the mine was then used for many different reasons, including a shelter in World War 2, a cheese storage center, and now, it is a subterranean theme park featuring mini-golf, bowling and rowing in the man-made lake.

According to Business Insider, the mine was ranked amongst the top 25 hidden gems around the world worth visiting, and over two million tourists come a year.

24 Radhuset metro station, Sweden

Talk to anyone who has to get through rush traffic in the morning in a major city and they will tell you it can be hell to get through. Well the Radhuset metro station in Stockholm, Sweden takes it that one step further, as this sculpture finish is made to look like the eternal flames and passengers are either descending deeper into out or on the positive side, escaping, depending on where you are in your commute.

According to CNN, it’s one of 90 subway stations in the city that are decorated by over 150 artists.

23 Coober Pedy, Australia

In Coober Pedy, the Desert Cave Hotel is of the many buildings in the city that are actually located underground, and this hotel room will definitely give you that cave-like experience with the lack of windows and cave walls.

A hotel underground!

According to CNN, the mining town on the edge of the Great Victoria Desert gets so hot in the summer, temperatures can reach 125 Degrees Fahrenheit, so the town of 1,695 people functions underground to keep cool. Everything from bars, to homes and even churches, rest under the Earth.

22 Bounce Below, Wales

Trampoline parks are popping up all over the place and are a fun outing to do with children.

But in Wales, they decided the indoor part of the trampoline park could be taken a step further, and put well underground, as a 176-year-old slate mine was converted into Bounce Below, a multi-tiered trampoline network that is suspended in a cavern the size of a cathedral.

According to CNN, it cost $920,000 to install the giant trampoline network, and hard hats are still required to be worn for safety.

21 Paris Catacombs, France

Above ground, Paris is one of the most beautiful cities, often called the City of Light. Below ground, it has some dark history and is the resting place for over six to seven million people, according to CNN.

That’s because Paris back in the 18th century was having a problem with overcrowded cemeteries, so to prevent it, they converted quarries into catacombs.

The catacombs are always 57 Degrees Fahrenheit, and today, you can book a tour that will cover 1.2 miles of the passageway, showing the underside of Paris.

20 Greenbrier Resort, US

While cold war history buffs get to see the Russian side of it, they can now see the United States side of it, as the Greenbrier Resort in White Sulphur Springs, West Virginia is available to the public.

It’s an amazing look inside the bunker that would have housed the US Congress in the event of an attack.

According to CNN, it was completed in 1961 and renovated in 2006 to be open to the public. One wing of the resort is over 112,000 square-feet square and the 25-ton blast door is still noticeable and a warning to the dangers that could have been.

19 Darvaza Gas Crater

This is a perfect example of why you don’t play with fire. The Darvaza Gas Crater goes down about 100 feet and is a natural gas field in Turkmenistan. The dangerous part is after an oil rig collapsed, scientists wanted to burn the methane gas off, so they lit it on fire, expecting it to last only a couple of weeks.

It has lasted over four decades. The crater, nicknamed the ‘Door to Hell’ has been burning ever since and turned into a popular tourist stop, as according to CTV News, over 50,000 tourists have visited the site since 2009.

18 Cave of Crystals in Mexico

The Cave of Crystals is located in Chihuahua, Mexico and in the main chamber there are giant selenite crystals. The largest one found to date is 39 feet in length and 13 feet in diameter and weighs 55 tons.

The cave is extremely warm however, with temperatures reaching 58 degrees Celsius, with 90 to 99 percent humidity.

It’s 980 feet below the surface, and because of the high heat, they had to close it down. According to the BBC, water pumps installed to keep the water out failed and the cave flooded again, leaving much of the cave still unexplored.

17 Underground Discharge Channel, Tokyo, Japan

72 feet below the largest city in Japan there is a massive pressure-adjusted water tank that looks more like a concrete cathedral than a water tank. There are 59 pillars that weight 500 tons each in the 580 foot long, 256 foot wide by 50-foot high channel that was built between 1992 and 2006 and is the world’s largest underground flood water diversion facility.

It is used only about seven times a year when heavy rains or typhoons hit the metro area, rerouting water away from the city.

When it’s not being used, according to CNN, there are tours three times a day, showing off the amazing accomplishment.

16 Salt Cathedral of Zipaquira, Colombia

Where is a perfect place to build a cathedral? How about 660 feet underground in a salt mine? That is exactly where the Salt Cathedral of Zipaquira is located in Colombia, according to CNN, which was built in 1950 and inaugurated in 1954.

It was dedicated to Our Lady of Rosary, the patron saint of miners, which only seems fitting.

The cathedral is a functioning church as well, and has over 3,000 people attending on Sundays, however, it has no bishop, so it is not an official status cathedral.

15 Pionen White Mountain Data Center, Sweden

Pionen is the former civil defense center for Sweden that was built into the White Mountains in case of a nuclear strike. But in 2008, it was converted into a data center, which rests below more than 30 meters of granite.

The data center is capable of withstanding a hydrogen bomb, although luckily, it has never been tested for it.

According to the London Associated Newspapers, the data center was the home to all of WikiLeaks, hosting their servers in 2010.

14 Yerebatan Basilica Cistern, Turkey

The Basilica Cistern in Turkey is the largest of several hundred ancient cisterns that are located beneath the city of Istanbul. It was built in the 6th century according to CNN and provided a water filtration system for the Great Palace of Constantinople.

It has been used a lot for Hollywood films, including in the climax of Inferno, the Robert Langdon trilogy movie.

Today, the cistern is lit up and easily accessible for visitors who want a peak back to the earliest years of Turkey.

Want to see what a top-secret military facility looks like? Well, now you can at the Naval Museum Complex in Crimea, which housed the USSR submarines in the underground lair during the Cold War.

According to CNN, the entrance to the complex is hidden in the Black Sea, though submarines could enter the complex safely.

The complex could withstand a 100-kiloton nuclear event, but today, they are less worried about that and more about showing people history through tours of the complex.

12 Down Street station, England

Under London, England there are more than 40 disused stations through the enter network. Down Street station is one of them, but has some history behind it, as according to CNN, before Winston Churchill had his Whitehall bunker built, his cabinet would meet in the unused station in the years leading up to World War 2.

Back then it was known as the Barn, and today, Transport of London has reached out to developers who want to turn it into bars and restaurants.

11 Cabinet Rooms, England

Speaking of the Whitehall Room, there are now open to the public as the Imperial War Museum, which allows visitors to trace the steps of Britain’s leader during the days of WW2. The cabinet rooms in England hosted 115 cabinet meetings according to CNN, mostly during Germany’s blitz, that saw the city attacked each night.

It was used around the clock until August 16, 1945. Today it’s a reminder of the lengths the British government had to go to keep their government safe.

10 Kariz-e-Kish, Iran

The Roman aqueducts are old, but the underground irrigation system in Iran is older, as according to CNN, the Kariz-e-Kish is 2,500 to 3,000 years old, and transported mountain water through subterranean channels across the island.

The tunnels were more than five miles long and were 50 feet beneath the earth.

Today, they have become a tourist attraction in a place that has little light and cool temperatures. But that hasn’t stopped people from taking in history in the underground city like atmosphere.

9 Wieliczka salt mine, Poland

The Wieliczka salt mine in Poland is now a UNESCO World Heritage Site and was a functioning mine since the 13th century until 2007 where it produced table salt, making it one of the world’s oldest salt mines in operation.

Today, the mine is currently one of Poland’s national Historic Monuments, as it includes four chapels carved out of rock salt.

Around 1.2 million people visit each year, with a wooden staircase taking tourists down to the 210-foot level. A three-kilometer tour takes guests through the corridors to see some amazing carpentry, brickwork, and chandeliers in the dining rooms.

8 Ruby Falls

Tennessee isn’t a place you really expect to see one of the most waterfalls in the world, but that’s because you have to look under the ground to find it.

The underground waterfall is 145 feet high and open to the public, and to make it somewhat of an attraction, the falls are lit by LED lights that change color to give it an amazing look, especially in the darkness of the underground cave it’s in. It was also designated a National Historic Landmark.

7 Edinburgh Vaults

The Edinburgh Vaults are a series of chambers formed in the arches of the South Bridge in Edinburgh, Scotland. The vaults were used as storage space and workshops for the South Bridge business and then were slum housing as well, though living conditions were not good at all, with no running water and lots of crime.

The vaults were then closed down, only to be discovered again in the 1980s by a Scottish rugby player according to the Sunday Herald.

Today, the vault hosts private events, weddings, dining and live music, though the BBC reported in 2009 that there was plenty of paranormal reports.

6 Louisville, Kentucky tunnels

For those seeking a thrill in Kentucky, perhaps it’s time to look underground for some fun. Below the streets of Louisville, there is a tunnel system that one served as storage for the Lakeland Asylum for the Insane.

But today, tourists can walk through the maze-like caves and caverns on rope bridges, or even hook themselves up to a zip line and rip through the cave. If you have the space, why not use it. Just be sure to wear a hard hat, because it is a cave of rock after all.