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

Cursed swimming pool left abandoned is now a favorite of filmmakers and ghost hunters.

A landscape decorated with enormous skull sculptures.

Cliffside houses provide a spectacular view from their perch above the valley.

A gravity-defying "devil's bridge" that has a surprising architectural feature for its stability.

Spanning the El Chorro gorge, this pathway used to be one of the most dangerous crossings in the world.

An enchanting monastery in the Spanish countryside appears lifted from a fantasy tale.

Wonderland replication in progress by one persistent man.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

A beautiful but toxic fountain of mercury.

Three bridges and one giant canyon make up this fantastic Spanish settlement.

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

This razorback ridgeline has doubled as a scenic drive since the early 1900s.

The remains of the dam that unleashed a 15-foot wall of water on Denver.

The scene of one of the darkest moments in American labor history has been left essentially untouched since the tragedy.

This Colorado hiking trail provides a small gold mine of abandoned gold mines.

Abandoned silver mine strewn with wrecked and twisted structures.

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

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

This naturally-sourced hot spring is now home to a clothing-optional resort.