King's Capuchins' Catacombs in Palermo. Thousands of mummified people from several centuries, lined up against the walls of the catacombs, monks and priests in their robes, people in their Sunday best, army officers in uniform, babies in their smocks... in various stages of preservation from dusty skeletons to looking like they're just asleep.
Food for thought--it certainly isn't light-hearted viewing. Not recommended if you're feeling sensitive or squeamish.