Campi Flegrei and Baiae

West of Naples the ground is a large caldera of craters, fumarole fields and hot springs, and it moves: bradyseism raises and lowers the land by metres over decades, visible on the columns of the Serapeum at Pozzuoli, where marine molluscs bored holes several metres above the present floor, showing the market was once submerged. Baiae was the empire's most fashionable resort, with bath complexes and villas; the same subsidence took part of it under the sea, and streets, mosaics and statue bases now lie in shallow water as an underwater archaeological park visited by glass-bottomed boat, snorkel or dive.

What you actually see

• The sunken city - Roman streets and mosaics in shallow water at Baiae.
• The Serapeum columns - mollusc borings marking former sea levels.
• The Solfatara crater - a fumarole field, currently closed to visitors.
• The Baiae baths - terraced bath complexes above the shore.

When to go

April to June and September to October; underwater visibility is best in calm settled weather and boat trips are cancelled in swell. Summer is hot and crowded.

Honest expectations

The Solfatara crater has been closed to the public since a fatal accident in 2017. Underwater visits depend entirely on sea conditions. Sites are scattered and need a car or several trains.

Nearby

Naples lies east; Cuma's Sibyl cave is north.