Black eggs, you say!? Don’t worry, they are regular chicken eggs.

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, Kurotamago (黒卵 lit. "black egg") — a local specialty of eggs hardboiled 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. (Wikipedia)