Like many preserved Roman sites it is underneath a church. In this case the Basilica of Sts. John and Paul on Clivo di Scauro. This by the way is an actual Roman street, little changed since the day when it was a sort of short cut from the Circus Maximus to the residential districts beyond the hill.
John and Paul were brothers, and officials in the court of the first Christian Emperor, Constantine the Great. When the brief pagan revival came in the form of Julian the Apostate (361-363) the brothers were martyred. Interest in the earlier structures beneath the current basilica led to excavations beginning in the 1880s.
What was uncovered was a maze of rooms, passageways, even a little street. The site is very nicely preserved with wall paintings and mosaics intact. After the Empire again became Christian the house was donated to the church and the existing Basilica was constructed, starting in 410 AD. The incorporation of existing structures was extensive and accounts for the remarkable preservation.
Some first rate wall paintings are on display.
A shrine traditionally associated with the original place of worship. I understand that this is called a "Confessio" and that the assorted Saints depicted might or might not represent John and Paul.
Nearby we find a reliquary, possibly for the remains of John and Paul.
A view of multiple levels. Dwelling places grand and humble, a street, some shops. There are also bathing facilities, a well and a nymphaeum. Roman archeology is complex.
Of course I had to peek into a store room where extra stuff found in the excavations is just sitting around.
I mentioned that excavations were mostly done in the 1880s. The main investigator was a Father Germano who was rector of the Basilica directly above this site. It looks as if the original lighting fixtures he put in are still there! I see that there are still candles in them and that they have been recently used. I assume this is for some sort of special occasion, in general your carefully conserved wall paintings would not be happy with prolonged exposure to smoke and soot!