Explore the largest pure gypsum deposit in the world, and go dune sledding while you're at it.

A sudden, striking cluster of hills south of Padua has been attracting visitors for centuries.

This seaside Italian village doesn't just look Escher-esque, it actually inspired the mind-bending artist.

According to the legend, this structure was built in a single night with the help of the devil.

Also known as the Temple of Poseidon, this is one of the best-preserved Greek temples in the world.

The only visible remains of this ancient Greek underground temple is its roof protruding from the earth.

The ruins of a 2,000-year-old Roman fishing village perched on one of the best beaches in Spain.

Single runway interrupted by a busy road that cuts across its middle.

Stroll through a wonderland of stupendous moss-covered trees.

A picturesque (all-natural!) beach in a landlocked state.

This enigmatic building features numerous architectural styles.

Two tall rocks sit at the center of this site, once the home of a large Ancestral Puebloan community.

Take a dip in the world's largest mineral hot springs pool.

A glimpse of a waterfall is reached by a steel catwalk along a slot canyon located in an Ouray city park.

Even in death, he's still your huckleberry.

The world's largest key collection features keys to the White House, Frankenstein's castle, and Hitler's bunker.

A downtown park built on top of unclaimed graves.

The largest source of fossilized insects anywhere.

This tea house was a hand-built gift from Boulder's sister city in Tajikstan.

This spectacular track has run continuously since 1882.

The highest bridge in America was built for an almost unnervingly small amount of money.

When ecosystems collide in the arid Southwest.

The largest self-built castle in the U.S., six decades in the making.

A breathtaking array of ancient Pueblo structures and artifacts counterintuitively preserved by neglect.