On my recent trip to Yogyakarta (Java, Indonesia) finding the underground mosque in the Taman Sari complex was my favorite experience, which was only possible with the help of a local guide.
During the mid-18th century, the Sultan of Yogyakarta began work on the Taman Sari Water Castle. Comprised of lavish gardens and pools, it also featured a bizarre man-made sea, connected beneath the ground with underwater tunnels and small island buildings. One of these island structures was used as a mosque, and was only accessible by underwater passage.
The tiny mosque, although basic, had all the necessary parts of a mosque including a mihrab, guiding worshippers toward Mecca. It also featured a series of staircases leading from the underwater entrances resembling MC Escher’s complex architecture work. Staircases lead up from five different doorways to a central platform and another staircase connects the five lower staircases to a higher doorway.
Today many of the remains of the great 17th century complex have been lost. The pools were emptied, which allowed for the discovery of many of the underground structures, but have destroyed the pristine castle quality. Human settlements have taken the place of the man-made lake, and much of the other buildings are ruins. In 1995, the entire complex was listed as a tentative World Heritage Site.