In the Basque sculptor Eduardo Chillida Tindaya Mountain, on Fuerteventura. Chillida's idea was to create a large empty void inside, with dimensions 50 x 50 x 50 meters, with an entrance tunnel of 200 meters and two skylights.
This reminds me of water parks on the Greenway now.I love the idea of creating "rooms" of water. Water sculpture "Appearing Rooms" installation by Danish artist Jeppe Hein. In front of the Festival Hall in London