Catacombs of Paris
Here is Les Catacombes de Paris. This was close to the hotel we were in while in Paris, and there was a constant long line of hundreds of people all day long to get in. So this is a very popular place to visit. We got advance tickets to get in, and it was something like I have never seen before. Millions of human remains have been stockpiled here underground. More info here if you are interested. What really struck me was the patterns and shapes they made with the bones. They really took their time on this.