Santa Maria della Concezione dei Cappuccini is known for its unusual and fascinating crypt, created after 1631. This site attracts attention for a very unique reason—its chapels are decorated with the bones of friars who once lived and worshipped there.
Inside the church’s crypt, visitors find a series of chapels where the remains of around 3,700 Capuchin friars are displayed. Instead of being buried in the ground, these bones are arranged on the walls and ceilings in artistic patterns. The displays include skulls, arm bones, and other skeletal parts, all carefully glued into place to form religious symbols, shapes, and designs.
The overall effect is both bizarre and memorable. The way the bones are used creates an atmosphere that is at once beautiful and haunting, leaving a strong impression on everyone who enters this remarkable crypt.
Source - https://en.wikipedia.org/wiki/Santa_Maria_della_Concezione_dei_Cappuccini