The deepest sinkhole in Central Europe comes with a grisly tale and an unusual nickname: “The Stepmother Abyss.”

Largest Kauri tree in New Zealand.

The platform atop this verdant volcano was built with the help of a royal elephant.

Highly spherical boulders on the shores of New Zealand.

A galaxy of glowworms—larvae of a gnat—hides deep in the belly of these caves.

One of the world's steepest streets seems to have houses sliding down it.

This strange geological landscape erupts with sudden bursts of water.

A Maori village obliterated by an 1886 volcanic eruption.

A glacier pocked with ice caves and surrounded by rainforests.

This electric green sulphur lake in New Zealand looks like a cartoonish radioactive dump site.

Dolphins, ancient clams and hundreds of waterfalls make this one of the world's top tourist destinations.

An expansive complex of subterranean tunnels is all that remains of one of Europe's most formidable medieval fortresses.

A little sculpture with a large wardrobe.

Hiding the longest subterranean river known in the world.

Climb inside an iron crystal magnified 165 billion times its normal size.

People have been living in the cave houses on this Italian hillside since the Neolithic era.

Southern Italy's spinning top village.

One of the largest caves in the world open to the public.

Virgil's many-mouthed gateway to the underworld.

This domed temple was built in a hidden cave mouth as a refuge for sinners seeking absolution.

The last moments of the ill-fated Pompeiians, frozen forever in plaster.

2300-year-old Roman road connecting the empire.

Stalactites and stalagmites in a beautifully lit cave.

Pompeii's less famous neighbor is still revealing her secrets.