“And when Herod would have brought him forth, the same night, Peter was sleeping between two soldiers, bound with two chains: and the keepers before the door kept the prison. And behold an angel of the Lord stood by him and a light shined in the room. And he, striking Peter on the side, raised him up, saying: Arise quickly. And the chains fell off from his hands. And the angel said to him: Gird yourself and put on your sandals. And he did so. And he said to him: Cast your garment about you and follow me, and going out, he followed him. And he knew not that it was true which was done by the angel: but thought he saw a vision. 10 And passing through the first and the second ward, they came to the iron gate that leads to the city which of itself opened to them. And going out, they passed on through one street. And immediately the angel departed from him.” –Acts 12.
St. Peter in Chains is unremarkable on the outside. On the inside, however, it contains a great treasure. The chains from two of St. Peter’s imprisonments. They fused together miraculously when Leo the Great held them together. Oh, and Michelangelo’s masterpiece (he was a sculptor, not a painter) the tomb of Julius II.
It was originally designed to be about 2/3 bigger. Still it is one heck of a tomb.
This is the guy who build St. Peter’s basilica more or less. You can thank him in the hereafter.