The six million skeletons hidden in over 150 miles of tunnels under Paris' streets

From the Eiffel Tower to the Louvre, Paris' top tourist attractions draw around 50 million visitors to the French capital every year.

But many travellers miss one of the city's more curious landmarks - because it's entirely underground.

Hidden beneath the streets of Paris is a labyrinth of tunnels with more than six million skeletons inside.

The Catacombs were first opened in the late 18th century when public health issues at Paris' cemeteries led authorities to move the skeletons to an underground site.

The last bones were put in the Catacombs in 1860 but the site was first opened to the public in 1809. The first visits were by appointment only but quickly became very popular.

While just a small section of the Catacombs is open to the public today, the entire network is thought to be around 174 miles long.

Nowadays, tourists can visit the site and the Catacombs gets around 550,000 visitors a year.

Travellers will need to descend 131 steps, 20m down into the 'depths of Paris' to reach the site.

Visitors then follow a 1.5km long route around the Catacombs which takes about an hour.

And while the Catacombs are open all year round, there's a particularly good reason to visit during summer.

Even if temperatures are heatwave-level outside, it's generally never warmer than 14 degrees inside the Catacombs, making the tunnels the perfect cool escape from warm weather.

As unusual as it may seem as a tourist attraction, the Catacombs have picked up a 4.1/5 star rating on Tripadvisor.

One reviewer writes: 'What a unique experience in Paris. It was an informative experience.'

Another person says: 'Weird but interesting. The bones were arranged and stacked skilfully.'

And another person reveals: 'This was my favourite part of my trip to Paris. I'm a nurse and a science lover, and am confident that anyone with great interest in history will enjoy visiting the Catacombs.'