Thríhnúkagígur: The only volcano on Earth where you can descend into a magma chamber

Three images of the inside of an empty magma chamber beneath Thríhnúkagígur volcano in Iceland. The walls are colored yellow, blue and purple.

QUICK FACTS

Name: Thríhnúkagígur, or Three Peaks Crater

Location: Southwest Iceland

Coordinates: 63.9984, -21.6989

Why it's incredible: The volcano hosts the world's only magma chamber that's accessible to humans.

Thríhnúkagígur is a dormant volcano near Reykjavík whose last eruption 4,500 years ago left a hollow magma chamber with bronze-and-indigo-colored walls. It's the only place in the world where people can climb into a volcano's plumbing system and explore the cavern that held sizzling molten rock before an eruption.