The Catacombs of Paris are a truly remarkable place, and if you've ever needed a reminder that everyone is the same, then a place where the skeletons of six million people remain should surely do it.
After a bunch of sink holes started collapsing buildings in Paris, people thought it'd be a good idea to maybe reinforce the foundations of the city, and that perhaps the mining of limestone from beneath the city could be responsible for the aforementioned destruction.
Whilst there's only a limited number of avenues with skeletons, there's a labyrinthine network of tunnels underneath the city.
Overall the Catacombs are awesome, but it's pretty depressing to see that some scumbags have vandalised some skulls. What would motivate someone to do that is beyond me.
If you're ever in Paris, definitely check it out.