Quinta da Regaleira
palaceThe most unique site in Sintra. The 27-meter Initiation Well — a spiral staircase descending into darkness — is unlike anything else in Portugal. But the entire estate is a symbolic labyrinth: underground tunnels connect grottoes to a lake, the chapel hides alchemical symbols, and the gardens are designed around Masonic and Templar mythology. You need 2 hours minimum. We've been four times and still find new corners of the garden we missed before.
Take the tunnel at the bottom of the Initiation Well — it exits at the lake grotto. Most people miss this and just climb back up the stairs.