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In Roman times, these 1st-century-BC ruins were part of a sprawling palace and spa complex. Emperors would entertain themselves and their guests in a series of lavishly decorated thermal baths that descended to the sea. Among the surviving snippets are exquisite floor mosaics, a beautifully stuccoed balneum (bathroom), an outdoor theatre and the impressive Tempio di Mercurio, its oculus-punctured dome predating Rome's Pantheon. The dome once covered a frigidarium (cold bath), located approximately 7m below the current water level.
To get here on public transport, catch the Cumana train to Fusaro station and walk 150m north to Via Fusaro. From here, the site is a 900m walk east along Via Fusaro. Alternatively, from Via Fusaro, you can catch a Monte di Procida–bound EAV bus to the site (services run roughly every 20 minutes Monday to Saturday, with reduced services on Sunday). This bus can also be caught in central Naples, at Piazza Municipio or Piazza Vittoria.