This incredible place is the (ex) church of San Felice and San Niccolò in via San Felice at the corner with via dell’Abbadia.
Walking down the street you can’t notice nothing but a dirty and dilapidated old portal and some sheets that cover the external stuccoes, but the beauty is hidden inside.
You can only unveil the mystery from the upper floors of the opposite building, from which you can see the church that is completely uncovered, probably because of a bombardment during WWII: the inner structure became some sort of beautiful arena / open-air theater, now used as a nest for birds. Have a look to the map below, the satellite view it’s really amazing!!
Below is the description on the plaque next to the portal:
“Church of San Felice and San Niccolò
Dates back to the XII century. It was rebuilt by Peter Fiorini in 1576 and renovated in 1753. From the original building only the facade remains, on which was placed an iron cross on the marble pillar, moved here from the road in 1732 (the cross is now kept in the church of Santa Maria of Charity). ”