This astonishing estate was built in 1904 to 1910, in the last days of the Portuguese monarchy.
The property once belonged to the Viscondessa da Regaleira, hence the name, but the house and gardens were built for António Augusto Carvalho Monteiro (1848-1920).
Monteiro, known as "moneybags " (Monteiro dos Milhões), had numerous estates but was always acquiring more. The house and gardens were created by Italian set-designer and architect Luigi Manini (1848-1936) and a host of sculptors, stonemasons, and craftsmen.
The estate is in Sintra, Portugal, on a steep hill. The gardens, grottoes, and so on are amazing.
The estate has an amazing web site, which you can read in English, with videos, virtual tours, and more. Looks well worth a visit.