Kaplica Czaszek

In Poland there's a chapel filled with skulls. The walls are lined with skulls. I touched one. The ceiling has skulls with crossbones. There's a table with the unusual skulls they found. Basically, in the area, there was a plague. Years later, flooding occurred, uncovering the mass graves from the plague. A priest thought this would be a good way of honoring the dead.

Here's the wikipedia page: Skull Chapel