To get to the catacombs, visitors are advised to take the metro and get off at the Denfert Rocherea station. At the entrance to the catacombs, there is a gate with a sign saying Arrte! C'est ici l'empire de la Mort which means "Stop! Here lies the Empire of Death".

It is usual to wait for up to 4 hours to get in because visitor numbers are restricted to 200 at any time and there are hundreds of them cueing at the entrance most of the time.

If the ominous sign and long cue is not discouraging enough, you have to walk down 130 steps 60 feet deep into the Parisian underground.

Narrow and slippery stone passages filled with musty, humid air will get you to the beginning of what definitely will be one of the scariest tours of your life.

From now on, its just you, dark spooky tunnels and never-ending masses of bones. The tour takes approximately 45 minutes and covers just a tiny 1.2 mile-long fragment of the catacombs.

Originally, the catacombs served as tunnels and caverns for stone mining in Roman times.

The stone mining continued without any limitations until the 15th century when the severely undermined city streets began to collapse and crumble.

At that time, nobody knew how long the tunnels were and where they led. Therefore, people started to map the labyrinth out and support the shafts. It still hasn't been mapped out completely but today, we know the catacombs are about 200 miles long

In the 18th century, Paris was facing a problem with overcrowded cemeteries. Plague and other epidemics had been decimating the city population and there was no more place to deposit the remains of the dead.

As a solution of this troublesome problem, the king ordered to move the remains from all the Parisian cemeteries to the catacombs. It took years to accomplish.

Soon after, some parts of the catacombs were opened to the public. Decorated with bones, these places became a popular amusement spot for then aristocracy. Many famous people including Napoleon Bonaparte and Otto von Bismarck visited the catacombs at that time.

People who have been exploring the uncharted areas of the catacombs are known as Les Cataphiles meaning the underground lovers.

There are dozens of entrances to the catacombs but most of them have been bricked up. Tourists can get there only through the official one at the Place Denfert Rocherea.

The city centre is undermined to such an extent that only a few large buildings were built.

Some of the bone arrangements are almost artistic in nature, such as a heart-shaped outline in one wall formed with skulls embedded in surrounding tibias.

During World War II, the tunnel system was also used by soldiers. German soldiers, for example, established an underground bunker in the catacombs below Lyce Montaigne, a high school in the 6th Parisian arrondissement

Walking through so many human remains can be a very disturbing experience. Some tourists even claim that they felt the presence of the skulls actually staring at them.

Over the years, many people have gotten lost and died in the catacombs. One of the most famous stories is the one about a man called Philibert Aspairt who got lost in the catacombs in 1793 and was found dead 11 years later.

Since most of the catacombs lie about 100 feet under the surface, lower than the Parisian metro, the temperature doesnt change throughout the year. It's always about 55 F.

In 2009, due to vandalism and theft of some skulls, the catacombs were closed from October to December.

In recent years, the catacombs have also become host to secret, illegal underground parties. Consequently, the area has been guarder by police patrol.

When walking through the catacombs you'll notice that the only bones visiable are arms, legs and skulls. Some of the other, more randomly shaped bones, have been used to create supporting walls in the collapsed and damaged parts of the catacombs.

Seeing so many human skulls, you cannot help but wonder about the identity of these people. Who were they? What did they look like? How did they die?

A 45-minute tour may not seem long but after spending 45 minutes among the dead, most tourists are happy to see the light of day.