Ripa contains the ruins of the Circus Maximus, the famed stadium that once held up to 250,000 spectators. Tiiber Island, the site of an ancient cult, now hosts summer concerts and films. Leafy Aventine Hill is home to posh villas, boutique hotels, churches and the Knights of Malta Priory, with a famous keyhole offering views of St. Peter’s. Tourists take playful dares at the Bocca della Verita (Mouth of Truth) altar.