The crypt or subterranean church of San Carlino repeats the ground plan of the main church, but in a more simple way. It remains unfinished. The altar niche has an 18th century fresco depicting Jesus on the Cross with the Virgin Mary and St. John. When I had struggled my way up to the church of San Carlino, I felt both warm and a bit tired. The crypt gave me a pleasant coolness. And the small chapel to the left intended to be Borromini's last resting place is still empty...