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Owakudani, or the Great Boiling Valley, is a volcanic zone with hot springs, sulfur vents, and a great view of Mount Fuji. It is also the best place in Japan to eat a black-shelled, longevity-enhancing egg while surrounded by pungent toxic gases.

The eggs of Owakudani turn black when boiled in the thermal pools—the sulfur and minerals in the water react with the eggshell, causing the color change. A gondola lift brings cartons of eggs up the hill for boiling, after which they are sent back down to be sold in packs of five. Due to the presence of hydrogen sulfide and sulfur dioxide in the air, visitors are allowed only a brief look at the cooking process.

Superstition holds that eating one of the eggs adds seven years to your lifespan—something to keep in mind when struggling through the sulfurous taste. If the black eggs of Owakudani don't faze you, try the Chinese delicacy known as Tongzi Dan: eggs boiled in schoolboys' frothy urine. 

Visit Atlas Obscura for more on the black eggs of Owakudani.

Exciting eggs around the world:

• This Brooklyn sewage plant's digester eggs have a crude and hilarious nickname
• The Easter Egg Museum, for when you want to celebrate the Resurrection regardless of the date
• It's colorful, it's fragile, it's Eggshelland!

Visit Atlas Obscura for more on the black eggs of Owakudani.