A temple for all gods or in greek: The Pantheon.
Now a church dedicated to Mary and the Martyrs,built more than 2000 years ago and in perfect state. I had to go twice since it was closed when I got there (this photo). I was able to visit it again and found it open. It has an amazing dome (picture to come) of 142ft. Just as comparison, the Capitol’s is 96 ft. in diameter.
On top of the dome there is a hole, know as oculus 7.8 meters in diameter and this is the only source of light.