Basilica di San Nicola in Carcere

This innocuous-looking 11th-century basilica, hidden behind scaffolding when we last visited, harbours some fascinating underground ruins. Beneath the main church you can poke around the claustrophobic remains of three Republican-era temples and a series of cells that once served as currency exchange offices. The temples, which were used as a prison in medieval times – hence carcere (prison) in the church's name – were incorporated into the church's structure as witnessed by the marble columns in the basilica's side.