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 is a popular tourist site for its scenic views, volcanic activity, and especially, Kuro-tamago (黒玉子^?) — a local specialty of eggs hard-boiled in the hot springs. The boiled eggs turn black and smell slightly sulphuric; consuming the eggs is said to increase longevity. Eating one is said to add seven years to your life. You may eat up to two and a half for up to seventeen and a half years, but eating a whole third is said to be highly unadvised.

Owakudani "Great Boiling Valley" is a volcanic valley with active sulphur vents and hot springs in Hakone, Kanagawa Prefecture, Japan. It is a popular tourist site for its scenic views, hot water flowing and steam rising is the best view you can see there, volcanic activity, and especially, Kuro-tamago — a local specialty of eggs hard-boiled in the hot springs. The boiled black eggs smell slightly sulfuric; consuming the eggs is said to increase longevity. Eating one is said to add seven years to your life. You may eat up to two and a half for up to seventeen and a half years, but eating a whole third is said to be highly unadvised.