This beautiful natural train tunnel is said to grant the wishes of visiting lovebirds.

Thousands of exquisitely carved stone water storage wells, hundreds of stone steps fill this exquisite medieval stepwell.

The tallest stationary dunes on Earth also happen to sing.

Partially collapsed lava tube and cave system complete with concert hall, underground pond, and unique albino crabs.

The hottest place on the planet.

Collapsing castle on the Hudson river was once the storage site of military surplus business.

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

This one-time health resort was used by aristocrats around the world.

A miniature train-ride through Slovenia's largest cave system.

Castle and secret tunnel withstood a siege until its owner was killed by the Holy Roman Empire, while sitting on the toilet.

A chain of 16 wondrous lakes formed as a result of the gradual dissolution of soluble layers of bedrock.

Extraordinary sculpture garden created by an eccentric English poet.

An underground mansion with fruit-bearing trees and grapes growing beneath the surface of central California.

Intensely colorful calcite pools in Southern China.

A New England curiosity cabinet, one hundred years on.

Japanese island famous for poison gas and fluffy bunnies.

Rare karst landscape eroded from a flat seabed.

Considered the birthplace of the Copper Age and Bronze Age, the river is tinted red from 5,000 years of mining.

Rocky Atlantic beach home to a stunning stone arch.

Traditional 11th-century outdoor tannery.

Tour the world's largest deep-hole dimension granite quarry, where you can view the plant where gravestones are made and roll a ball down the outdoor granite bowling alley.

The "original web site," this farm in Northern Vermont encourages orb-weaver spiders to build their daily webs, and then sells the preserved masterpieces.

This fantastical house shaped like a seashell brings aquatic design to architecture.

An indigenous take on European design creates a stunning visual overload.