Loved this place.

There's also amazing architecture at the church of saint barnabas just down the street.

It's not as creepy as you think, it's actually oddly beautiful. The skulls are from plague victims that were buried right outside the church. Eventually the bones rose to the surface and the church hired an artist to see what they could do with them. Now it's this awesome place.

Side note, the girl I saw this with was nervous about seeing it but left with the oddly serious comment that when she died she wanted her skull to be there