Sounds like Basilica of San Clemente[1][2]. One of the many many many "hidden" gems of Rome. Highly recommend visiting it!

Or you can go on a virtual tour[3]

[1] https://www.basilicasanclemente.com/eng/

[2] https://maps.app.goo.gl/zpXpQuxQLUvE5TLA9

[3] https://www.basilicasanclemente.com/eng/a-virtual-tour/