The word city brings many thoughts to mind. Usually, when we think of cities we think of large areas containing huge buildings. However, there are many cities that are just the opposite. There are many cities that have been built into the ground instead of up into the air. The reason for these cities varies from place to place but they are typically old and historical. Now they serve as tourist attractions and some are even still functioning cities. These cities aren't all old, however, some are new and high tech and feature everything a modern city does.

These amazing places aren't very known to people who spend a lot of their time on the surface of the Earth. Did you know there is an underground city in Chicago? There is also a fully functional city underground in Japan. Who knew? These underground cities are like taking a trip to another world, and when you emerge you will probably be happy to see the sun again. Many of the places on this list were also built as protection from things like nuclear weapons. These places have now been abandoned or turned into something less disturbing.

20 Henan, China

The small town of Henan located in China is a set of people who have decided to live in a series of interconnected cave systems underground. The underground part of Henan is said to have over 10,000 homes and a whopping 3,000 people who still live in the Henan Caves to this day, according to dailymail.com. Many may think that the small town is dangerous to live in especially by today's standards. However, the cave system is a surprisingly high tech area with things like earthquake-resistant structures and the fact that the caves can sustain power. The caves can even house vegetation on the roofs of the cave houses.

19 Osaka, Japan

Japan is known to keep changing the game when it comes to just about everything. For example, they do innovate when it comes to technology. One example of this is the underground city of Osaka. The underground city is very popular among residents and tourists and always has loads of people walking through it. There is even a shopping district to Osaka in which residents and visitors can visit many malls and restaurants. Osaka is the best case scenario when someone says "let's build a city underground". Tourists who have visited Osaka claim that the city is amazing and it feels like they are in the underworld.

18 Ellora, India

Ellora is a set of many tunnels located in India. When you first enter Ellora, the tunnels are wide but as you go further into the tunnels they become smaller and smaller until no one can fit through them. Some of these tunnels are said only to be 1 foot wide but reach to be 40 feet deep. Many people believe that the tunnels are connected to a bigger underground city but no one is sure as no one has ever been able to travel that far in the caves. On the outside of the caves, there are large structures that are amazing to look at if you aren't the spelunking type.

17 Bonifacio War Tunnel, Philippines

Bonifacio War Tunnel was also known as Fort McKinley, which was a tunnel system that housed the American government officials under the rule of General MacArthur, according to lifestyle.com. During WWII the tunnel was used to protect the officials during the attacks. It was being expanded during the war until the Japanese got a hold of the tunnel and continued to expand on it. It is rumored that General Tomoyuki Yamashita used the tunnels as his personal quarters after the American defeat. Now the tunnel remains in poor condition and there are talks of the tunnel system being changed into a septic tank.

16 Pedway, Chicago

If you thought Osaka, Japan was impressive, wait until you take a look at Pedway in Chicago. The modern underground city is actually not known to a lot of people and is a fully functioning city. Pedway has around 40 blocks, all of which have varying restaurants and stores. Pedway connects over 200 different buildings and over 60 businesses according to the city of Chicago's official website. The city itself can be a bit daunting and it can feel as confusing as walking through an airport looking for your gate, but there are plenty of signs to help find your way around.

15 Underground City, Amazon Jungle

In the deep jungle of the Amazon, there is an unnamed underground city that is being protected by the indigenous people that live there. Anyone who wanders close to the city is quickly turned away by the guards outside the city. It is rumored that no one in civilization knows where the city is exactly located. The city is said to be filled with riches and there is even a large temple there. There have been several people who have searched extensively for the city and filmed their process in a documentary format, according to a website known as Documentary Heaven.

14 Bucharest, Romania

The Bucharest tunnels are fairly unique when it comes to underground cities. The Bucharest tunnels were originally just a set of abandoned tunnels and sewer systems until a group of orphans made it their home. The children eventually grew up and still reside in the tunnels beneath Bucharest. The entryway to the tunnels is a small hole in the ground in the middle of a heavy traffic road. The people that live down there rarely see the light and have even started a small civilization in the abandoned sewers of Bucharest. It is a hard life seeing as there is no natural light or any way to get natural resources. One person's story of living in the tunnels was covered by National Geographic and can be found here.

13 Reso, Montreal

Reso is a hidden underground city located in Montreal and is the biggest of the underground cities we have covered so far. Similar to Osaka and Pedway, Reso is a large commercial city full of hotels, restaurants, and other businesses. The whole city of Reso is connected via the metro system already in place in Montreal so you won't have to worry about travel in Reso. The best part of Reso is the fact that it is a great place to visit during the winter months of the harsh Canadian weather due to its warmth of being contained underground.

12 Subtropolis, Kansas

Subtropolis is a whole business district located inside a small hill in Kansas City. Subtropolis started from small beginnings as most underground endeavors have. The hole that used to be Subtropolis was originally a mining area for Kansas City and was plentiful in resources for the city, according to huntmidwest.com. Since then there was a large area left behind from all of the mining and it was then transformed into a small business district where many companies founded their headquarters. There is a lot to Subtropolis, including a room where movie producers send copies of their films for safe keeping.

11 Mamata, Africa

Mamata started as a simple hole in the ground that went a little far. Mamata was created by people digging small holes into the side of the area they dug and eventually these small holes turned into rooms which turned into homes for some people. It originally helped the locals escape the extreme heat of the area. The hotel located in Matata was used as the setting for Luke Skywalker's home in the Star Wars films. The place is now open to tourists and if you want to stay the night it won't cost all that much. That is right, you can sleep in the same place as Luke Skywalker for 20 bucks a night!

10 Burlington Bunkers, Britain

The small area known as Burlington was originally conceived to protect the British government. This was during the 50's when there were threats of nuclear war and the best way to avoid this was by digging underground. Burlington was originally made from a quarry and housed over 4,000 government officials and stretched to be around 240 acres, according to Business Insider. The hidden city maintained itself with different businesses like pubs and hospitals and even an underground lake. Burlington officially ended in 1991 and the government officials who were housed there were brought back to their families.

9 Shanghai Tunnel, Portland

Sometime in the 1800's, a tunnel was made in Portland Oregon for the only purpose of transporting goods from importing ships to local businesses to avoid traffic. However, the dream of having this tunnel be operational fell flat as the tunnel became a hot spot for crime in Portland. The tunnel has since fallen into abandonment and is sometimes still the place for crimes in Portland. It is also said to be haunted by a few people who have explored the tunnel system, but that is solely a rumor. This rumored sparked the interest of famous ghost hunting team known as the Ghost Adventures crew and they filmed an episode in the Shanghai Tunnel.

8 Giza Plateau, City Of The Gods

The mystery surrounding Giza and the pyramids is considered one of the seven wonders of the world. The Giza Plateau is also known as the Pyramid of Khufu and the mystery surrounds the inside of the pyramids. Many people believe that there is a hidden city under the pyramids and the pyramids are used as entryways to this large city. The pyramids themselves are impressive works of architecture which lead many to speculate how they got there. All the mysteries that surround the pyramids makes the actual truth behind the pyramids even muddier.

7 Moose Jaw, Saskatchewan

Moose Jaw, Saskatchewan is a small town in Canada and its winter months are known to be colder and longer than other places in Canada. The cold weather was becoming more and more of a problem for people who had to travel to work. The Canadian government decided to fix this problem by building a series of underground tunnels to keep workers warm on their way to and from work. The area quickly became a central hub for crime, such as gambling. This gained the attention of world-renowned criminal Al Capone according to atlasobscura.com.

6 Setenil De Las Bodegas, Spain

Setenil De Las Bodegas located in Spain is a city that was built into the side of a mountain and features a large boulder over the top of the city. So technically this isn't underground in the same sense as other entries, but it is under a rock so it counts. Setenil De Las Bodegas is a popular place in Spain right now due to its uniqueness in its architecture. The town currently houses around 3,000 people according to feel-planet.com. Another plus to visiting Setenil De Las Bodegas is the food that is served here. It is one of the reasons the place is so popular with tourists.

5 Beijing Underground City, China

Similar to other entries on the list, the Beijing Underground City was first formed after nuclear threats were directed toward China. Chairman Mao Zedong ordered parts of the population of Beijing into the underground parts of the city according to atlasobscura.com. The entire underground area was able to house around 40% of Beijing's total population and the underground area was a functioning town complete with restaurants, schools, and other businesses. The area underneath Beijing is now mostly abandoned but is still filled with remnants from the time almost half of Beijing lived underneath the city.

4 Kish Underground, Iran

Kish is known for its beautiful islands, but we aren't talking about islands today. Underneath Kish is a six-mile-long subterranean city that was built upwards of 2500 years ago according to ancient-origins.net. The main reason the underground area was built was to store water and purify water. While Kish sees a large number of tourists due to its beautiful islands, the underground part of Kish gets little to no love. Most of the areas in Kish Underground have been restored and it is an interesting dive into ancient history. Just remember to be prepared to walk for a while in a claustrophobic area.

3 Coober Pedy, Australia

Coober Pedy is known to be one of the hottest towns in the world and it is almost uninhabitable due to the climate. There are around 1,695 people living in Coober Pedy and it is known as the opal capital of the world according to their official website. The way the residents get around the heat is by digging their homes into the grounds in order to stay cool and comfortable in their homes. Coober Pedy has become so popular for its underground homes that they have even built different businesses down there, such as a museum and even a small golf course.

2 Wieliczka Salt Mine, Poland

Wieliczka Salt Mine is one of the oldest salt mines that are still in operation in the world. The salt mine started in the 13th century and supplied salt to nearby Poland. The mine is very long and deep and has even started its own community inside the central parts of the mine. The mine even has four different chapels to use by guests and workers. In 1996 due to a flood, the salt mine officially closed down salt production but it is still in operation as far as its amenities are concerned. The mine gets around a million people visiting it each year.

1 Darinkuyu, Underground City, Turkey

This underground city was actually found by accident in 1963 when a family accidentally discovered it when renovating their home. According to National Geographic, the underground city of Darinkuguyu stretches to be 11 layers into the earth reaching bedrock. The town has many businesses that include shops, and other interesting things to explore like tombs. The city houses over 20,000 people and was able to be done thanks to the brilliant ventilation system that was implemented into the underground city. The city even has access to clean water thanks to wells being placed throughout the tunnels.