Roman streets you can swim down. Intact mosaic floors, marble columns, statue bases, the Villa dei Pisoni, a nymphaeum with…Roman streets you can swim down. Intact mosaic floors, marble columns, statue bases, the Villa dei Pisoni, a nymphaeum with copies of its statues set back in place, and the road to the Portus Julius naval harbour, all in 5-14m of water. Snorkellers can see much of it; there are also glass-bottom boat tours for non-swimmers. Baia was the Las Vegas of the Roman Empire, the resort where Caesar, Nero, Hadrian and Caligula kept pleasure villas, and where Agrippina was murdered on Nero's orders. It sank not by earthquake but by bradyseism, the slow rise and fall of the ground over the Campi Flegrei supervolcano, which dropped the whole coastline into the sea by the 8th century. Anchorage: Anchor in the Bay of Baia; Naples and Procida nearby. Marine protected area, moorings and licensed guides required. Hazards: No site-specific hazards noted, brief normally. Plus