Quinta da Regaleira is an estate located near the historic center of Sintra, Portugal. It is classified as a World Heritage Site by UNESCO within the "Cultural Landscape of Sintra". Along with other palaces in this area (such as the Pena, Monserrate and Seteais palaces), it is one of the principal tourist attractions of Sintra. It consists of a romantic palace and chapel, and a luxurious park featuring lakes, grottoes, wells, benches, fountains, and a vast array of exquisite constructions. The palace is also known as "Palace of Monteiro the Millionaire", from the nickname of its first owner, António Augusto Carvalho Monteiro.
The park contains an extensive and enigmatic system of tunnels, which have multiple accesses including the grottoes, the chapel, the Waterfall Lake, and the "Leda's Cave" beneath the Regaleira Tower. Their symbolism has been interpreted as a trip between darkness and light, death and resurrection. The "Initiation Well" or "Initiatic Well" (sometimes referred to as the "Inverted Tower") is a 27 meter staircase that leads straight down underground and connects with other tunnels via underground walkways. A similar structure is the Pozzo di S. Patrizio in Italy.