Ōwakudani (大涌谷, lit. "Great Boiling Valley") is a volcanic valley with active sulphur vents and hot springs in Hakone, Kanagawa Prefecture, Japan. It was created around 3,000 years ago, as a result of the explosion of the Hakone volcano.
It is a popular tourist site for its scenic views, volcanic activity, and kuro-tamago (黒卵, lit. "black egg") — a local specialty of eggs hard-boiled in the hot springs. The eggs turn black and smell slightly sulphuric; eating one is said to add seven years to your life.
Upon seeing the hellish scenery when Koubu Daishi visited Owakudani more than a thousand years ago, he offered prayer to Bodhisattva. The Enmei-jizo in Owakudani is said to have its origin in the prayer.