Catacombs embody a dark, but nevertheless unique, part of human history. Every year millions of people travel overseas to visit the systems of underground tombs where countless bodies are preserved. Although a chilling experience,  it also allows visitors to recognize the historic burial practices.

RELATED: Afraid Of The Dark? Here's 10 Places We'll Seriously Struggle (10 We'll Absolutely Love Instead)

Each catacomb tells its own story and reflects a precise element of world history (though it is up to you to decide if you're brave enough to visit). If you are amongst the courageous, then you may enjoy this list of some of the world's creepiest catacombs. Visit at your own risk!

10 St Paul's Catacombs (Rabat)

Nestled under the old Roman city of Rabat in Malta, the St Paul's (or Rabat) Catacombs reflect the distinctive features of the town's history. Originally, the popular and macabre catacombs were part of the ancient Greek city of Melite. The site was discovered by a prominent Maltese archeologist, Antonio Annetto Cuarana, back in 1894.

The catacombs host over 30 underground tombs, of which 20 are open to the public. Its inner walls reveal multiple painted illustrations and written messages, along with free-standing burials. What makes this cringe-worthy catacomb so interesting is that the burial site shows evidence of Christian, Jewish, and Pagan graves with no apparent division, but instead a side-by-side setup.

9 Capela Dos Ossos

The words Capela Dos Ossos translate to "Chapel of Bones," and for good reason. Located in the city of Evora in Portugal and considered one of the best city monuments, the underground chapel owes its name to its walls, which are fully covered in human remains. The artifact-filled space was built during the 16th century, by a Catholic priest whose aim was to push visitors to reflect on life's transience.

RELATED: 25 Images Of The Most Questionable Sculptures

Another creepy facet of this lengthy burial site involves the several hanging skeletons which may be spotted during a visit. Additionally, scriptures can be found across the walls, including a poem which reflects on the concept of human existence.

8 Skull Chapel

The Skull Chapel is a 1776-built monument in the Polish town of Kudowa. The chilling catacomb is riddled with skulls on its walls, floors, ceilings, and foundations. Moreover, the burial site hosts the graves of countless individuals who perished during a set of wars including the Thirty Years' War and Silesian Wars. Furthermore, some of these remains belong to victims of cholera, syphilis, plague and simple starvation.

RELATED: 12 Tombs Worth A Visit Today (13 We Should Avoid Completely)

The gravesite came to fruition after gravedigger J. Langer and J. Schmidt, an officer of the church, were inspired by the Capuchin cemetery during a visit to Rome. To make matters creepier, the very skulls of those who helped build the catacomb are in there too.

7 Paris Catacombs

Undoubtedly the most famous catacombs there are, this grave site expands under the City of Lights. The underground ossuaries, which date back to the 1770s, were created in an effort to reduce the overwhelming number of above-ground cemeteries. It holds more than six million people inside! Prior to becoming the popular tourist attraction it is today, the site was used to host parties, concerts, and private events.

RELATED: 10 Of The Most Haunted Places To Visit

The Paris Catacombs were subject to several rumors throughout the years, including the endless ghost stories tied to its name. Accordingly, the tunnel network is large, complex and easy to get lost in. Hence, the rumors of trapped souls still crying out for help are probably inspired by real events!

6 Odessa Catacombs

The Odessa Catacombs are a true labyrinth. Located on the outskirts of Ukraine, the underground network encompasses basements, drainage tunnels, natural caves, storm drains and more. Furthermore, it is one of the largest urban labyrinths in the world. Its complexity, much like its dark, tiny spaces, is what makes these catacombs extremely sinister.

RELATED: 10 Haunted Houses To Go To... If You Dare

Moreover, reports of individuals walking into the catacombs and getting lost are very common. These poor people eventually die of hunger or dehydration. As such, much like the Parisian catacombs, this underground site is also the focus of many ghost stories.

5 Znojmo Catacombs

Burrowed beneath the historic homes of Znojmo in the Czech Republic, these catacombs were built by townsfolk for defensive purposes. The underground system dates back to the 14th century and notably expanded in the 15th century. Its elaborate labyrinth set-up was orchestrated by the city's inhabitants, to protect themselves from invaders.  Moreover, the subterranean caverns consisted of an intricate development in which cellars connected to house chimneys.

RELATED: 25 Images Of Ghost Towns That Everyone Forgot About

There were also traps in case invaders found a way in. citizens of Znojmo could hide in the caverns during invasions, to make the town above ground look deserted.

4 Palermo Capuchin Catacombs

The Catacombs of Capuchins are without a doubt one of the most macabre tourist attractions there is. The burial site is nestled under the southern Italian city of Palermo in Sicily. It is a historical wonder riddled with well-preserved artifacts, which include dead bodies.

RELATED: 8 Egyptian Mummies In Good Condition Found Near Cairo

The ghoulish site was once owned by monks, who came up with the idea of a mummifying practice. As such, numerous bodies are preserved to perfection to this day (though only the wealthy could afford the costly practice at the time). Some of the bodies found herein are embalmed, while others are hung from the walls in a standing position. To add to the catacomb's uniqueness, the bodies frequently undergo costume changes as well.

3 Petrovaradin Catacombs

The underground catacombs sit beneath the fortress of Petrovaradin, located in Novi Sad, the second largest city in Serbia. The dark and silent halls of the buried monument are not for the faint of heart. However, the buried network of tunnels is believed to host a series of uncovered treasures, for those who dare to search for them.

A guided tour is strongly recommended. The labyrinth tunnels are filled with history and chilling legends, which a guide will be able to elaborate on for you.

2 St. Stephen's Catacombs

These lengthy, dark and cryptic catacombs can only be visited with a knowledgable guide. The underground burial site resides directly below the St. Stephen's Cathedral in Vienna. Much like the other creepy catacombs in this list, bones line the walls and are stacked high within these buried caverns.

The catacombs served as the grave site of Austrian rulers, members of the clergy and high-ranking nobility. The remains of 11,000 people are found in the old crypt, which dates back to the 1700s. In addition, only a few lights have been installed underground, which is why a guide is required.

1 Hal Saflieni Catacombs

This architectural marvel is a three-story underground complex which dates back to 4,000 BCE. The Hal Saflieni Catacombs are found beneath the city of Paola in Malta and were discovered accidentally by a stonemason in 1902. The crypts are believed to have been a place of sanctuary, which was then converted into housing for the dead.

The underground networks are divided into chambers with names like Snake Pit and the Holy of Holies. Moreover, the population of dead bodies is currently set at 7,000 Maltese people, all of whom passed during the prehistoric era.

NEXT: 10 Must-See Cathedrals in Europe to Add to Your Travel Itinerary