Just a few miles west of Naples (and easily reached by train), the ancient seaside city of Pozzuoli is probably best known for its bradyseism, a raising and lowering of the Earth’s surface due to underground volcanic activity. Many sites remain from Pozzuoli’s days as an important Roman port, including the Macellum or Temple of Serapis, which for many years was submerged under water. The Flavian Amphitheater (Italy’s third-largest) and the Cathedral of Rione Terra are other popular attractions.