Home to several national museums and a major zoo, as well as numerous temples and shrines, Ueno Park is one of the most popular tourist attractions in Tokyo. You’d think it's been explored by tourists all over, and you couldn’t have been more wrong.

The western portion of the park is home to the Shinobazu-no-ike, a lotus-covered natural pond; and at the heart of it is an artificial island built in the mid-17th century to accommodate the Benten-dō temple, modeled after the sacred island of Chikubu on Lake Biwa.

Originally, the temple was to be established on Shōden-jima, a tiny natural island on the Shinobazu Pond whose name roughly means Ganesha Island, but it was deemed too small for such purpose. It is a fascinating site that still exists, yet virtually unknown despite being located in Ueno Park. How come?

The thing is, the island only opens to the public once every 12 days, on the Day of the Snake—likely because the goddess Benten is associated with snakes. Even on the days it is open, the island is so tiny that visitors may not realize that it is an island.

Accessible via a stone bridge, the island is home to a torii arch, a fox statuette, a variety of shrinelets and religious stelae, as well as a statue of En-no-ozuno, a 7th-century mystic known as the founder of Shugendō asceticism. Intriguingly, the statue is placed so that it faces the Shinobazu-no-ike, and only lucky visitors to Shōden-jima gets to see its backside, which is designed to look phallic.