Quinta da Regaleira is an estate inside a World Heritage protected landscapenear near Sintra, Portugal. The castle itself is a popular tourist attraction but there's more to it beneath the ground.
Two wells spiral deep into the earth like inverted towers. The wells were never used, nor intended for water collection, but for secretive initiation rites. The larger one contains a 27-meter spiral staircase with several small landings. The spacing of these landings, combined with the number of steps in the stairs, are linked to Tarot mysticism. The smaller well contains straight stairs that connect a series of ring-shaped floors to one another.
In addition to the wells there's also various caves, grottoes, tunnels and other monuments located around the castle park.