One of Europe's most mysterious landmarks, the bewitching Quinta da Regaleira in Sintra, Portugal was built by an eccentric tycoon with a penchant for the occult. Inspired by alchemy, the Knights Templar, Freemasonry and more, the castle is peppered with esoteric symbols and curious design enigmas. But the estate's subterranean secret concealed some 88 feet below the ground is its strangest and most mysterious feature...

Click or scroll through to explore the magnificent estate inspired by the occult and decode its many puzzles.