The Thermae of Constantine (Baths of Constantine), the Roman bathing complex, dates from the 4th century AD. Of the once-extensive series of buildings, which resembled a palace, only the Caldarium (warm bath) and parts of the Hypocaust (underfloor heating) and the Tepidarium (warm air room) remain. The Thermae of Constantine has been listed as World Heritage Sites since 1981.
References:The Villa d'Este is a 16th-century villa in Tivoli, near Rome, famous for its terraced hillside Italian Renaissance garden and especially for its profusion of fountains: the extraordinary system contains fifty-one fountains and nymphaeums, 398 spouts, 364 water jets, 64 waterfalls, and 220 basins, fed by 875 meters of canals, channels and cascades, and all working entirely by the force of gravity, without pumps. It is now an Italian state museum, and is listed as a UNESCO world heritage site.
Tivoli had been a popular summer residence since ancient Roman times due to its altitude, cooler temperatures and its proximity to the Villa Hadriana, the summer residence of the Emperor Hadrian I.
The Villa was commissioned by Cardinal Ippolito II d'Este (1509-1572), second son of Alfonso I d'Este, the Duke of Ferrara and grandson of Pope Alexander VI, along with Lucrezia Borgia.