We are going to meet across the street from the church of Santa Maria in Cosmedin (where the mouth of Truth is) by the round temple (of Hercules). The first place we will explore was a Mithraeum, hidden behind a gate, at the end of a tiny alley, under an anonymous building, 14 meters (42 feet) underground. Mithraic religion was a 'competitor' of Christianity, a very secretive religion of which very little is known. This extremely little known religion, secretive, which was practiced underground disappeared as Christianity prevealed and took over (not always peacfully) other faiths. This very special place will open solely for us. We are then going to move on to San Clemente, the most extraordinary church in Rome. Once out of there you will surely start wondering what it is hiding under every step you take. We will then proceed to another hidden treasure on (or rather under) the Coelian Hill: once apartment block then villa this building was demolished and dismanteled to make room to a church, the bell tower is sitting on the remains of a temple, the street still shows traces of little shops which have now disappeared. So Rome has transformed, many times, the best way to really see how far below the original (if there is an original one) is, is to go down and see it with your own eyes. The church of San Clemente is a perfect example of lasagna! As we proceed in our exploration of its multiple underground layers we will analyze and see and touch with our own eyes how much the city has changed, from pagan to christian, from public to private, from ancient to modern, adapting and shaping itself according to changed needs, interests, faiths. This is a truly fascinating way to discover Rome.