In antiquity this whole area was the Palatium Baianum (the Palace of Baia), dedicated to otium (leisure) and the residence of emperors from Augustus to as late as Septimius Severus in the 3rd century AD. At the park's ticket office, you should receive a small site map, and information panels in English are posted at strategic intervals. The first terrace, the Villa dell'Ambulatio, is one of the best levels from which to appreciate the site's topography: the whole hillside down to the level of the modern road near the waterfront has been modeled into flat terraces, each sporting different architectural features.
While up on the first terrace look for the depictions of dolphins, swans, and cupids in the balneum (thermal bathing, Room 13), and admire the theatrical motifs in the floor mosaic in Room 14. Below the balneum and inviting further exploration is a nymphaeum shrine, which can be reached from the western side. Make sure you get down to the so-called Temple of
Mercury, on the lowest level, which has held much fascination for travelers from the 18th century onward. It has been variously interpreted as a frigidarium and as a natatio (swimming pool) and is the oldest example of a large dome (50 BC–27 BC), predating the cupola of the Pantheon in Rome. (Test the rich echo in the interior.) In summer the site often provides an unusual backdrop for evening concerts and opera performances. The site office (848/80288) or the tourist office website (www.infocampiflegrei.it) will have information about them.