For fans of the macabre, this is a must. After descending some 100 steps, you’ll walk through roughly 1 mile of underground galleries and impressively stacked piles of bones in one of the world’s largest ossuaries. The visit takes about 45 minutes, and it’s pretty chilly down there, so be sure to dress warmly. We also recommend buying a ‘skip-the-line’ ticket (29€ for adults with audio-guide included, or 5€ for kids) online ahead of time to avoid the often hours-long wait to enter! Unfortunately, the catacombs aren’t accessible to those with reduced mobility.