Quinta da Regaleira is a palace and estate located in the hills surrounding the historic center of Sintra, Portugal. It is classified as a World Heritage Site by UNESCO. It is also known as the "Palace of Monteiro the Millionaire," from the nickname for its first owner, António Augusto Carvalho Monteiro.

Carvalho Monteiro, with the assistance of Italian architect Luigi Manini, designed the 4-hectare estate with the palace, luxurious gardens, lakes, grottoes and enigmatic buildings, believed to hide symbols related to alchemy, Masonry, the Knights Templars, and the Rosicrucians. The architecture of the estate evokes Roman, Gothic, Renaissance and Manueline architectural styles.