This Initiation Well at Quinta da Regaleira near Sintra, Portugal, one of several connected by tunnels, was never used for water; rather, it was the site of Tarot initiation rites. While beautiful and intriguing, the first thing that ran through my mind when seeing this picture was this:
Playing in the World Game 
Fascinating structure. Is there a surface entrance?
Not sure. I’d love to explore that complex.