
Dating back to Roman times the
Catacombs of Paris is one of the most surreal experiences you can take while on a tour of Paris. For as little as $3 euro you can walk the 2 km (1.2 miles) of tunnels that are literally lined with human bones from some six million Parisians.
As the Paris population grew in the 1700's the number of cemeteries didn't. As disease spread due to improper and cramped burials the police chief decided to condemn all the inner city cemeteries and move the remains discreetly to a renovated section of Paris' abandoned quarries.

The catacombs isn't just skulls and bones. There is also the occasional open area.

The actual tunnels stretch for hundreds of miles underground only a tiny portion is open to the public. It's an offense to venture into the unsupervised areas. The map below shows the full extent of the tunnels.
Fun Fact: In 2004 a
secret cinema was discovered by police who stumbled upon the make shift cinema complete with projection screen and seating by accident during a training exercise.
You can also visit the
Catacombs of Rome which contains artwork dating back to 400 AD.