The small church at the corner near the main entrance to San Callisto is widely known as the Church of Domine Quo Vadis, though this is not its official name. Its reputation comes from a famous legend connected to Saint Peter, one of the most important figures in early Christianity.
According to tradition, this church stands on the very spot where Saint Peter, fleeing persecution in ancient Rome, had a powerful vision. As Peter tried to escape the city, he saw the risen Christ and asked him, "Domine, quo vadis?" which means "Lord, where are you going?" This moment is said to have inspired Peter to return to Rome and face his fate.
The building that stands today was constructed in 1637. Visitors who step inside will find a special relic: a copy of a stone that displays the footprints of Jesus. The story goes that these marks were left when Christ appeared to Peter. The original stone, however, is preserved in the Church of San Sebastiano, which is located further along the historic Appian Way.
Source - https://en.wikipedia.org/wiki/Santa_Maria_in_Palmis