The Roman city was the birthplace of various emperors and is home to one of the empire's most impressive architectural feats.

Spanish architects used seized Muslim gravestones to rebuild parts of the fortress.

This magnificent castle grew from a small Moorish fortress, and reportedly inspired two iconic Disney castles.

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

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

Take a self-guided tour through one of Colorado's most elevated mining districts.

A dangerous narrow-gauge railroad once traced a route through this striking canyon.

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

These pretty kitties killed and ate as many as 135 railway workers.

This surprising gem is a world-class archeological museum hidden at the University of Chicago.

Years of archaeology, just chillin' by the water cooler.

This historic hotel invented the chocolate brownie.

A gothic church spire sits atop this skyscraper, the tallest church in the world.

This rare vessel mixed luxury with labor before being converted to a museum and sometimes haunted maze.

The watery grave of an impractical idea.

This picturesque cliffside beacon no longer calls to sailors but shines once a year in honor of a famous shipwreck.

Home to the Amorphophallus titanum "Corpse Flower," which is among the largest flowers in the world and also smells powerfully of rotting flesh when in bloom.

This massive stained-glass masterpiece is thought to be the largest Tiffany dome in existence.

Oldest building in California still in use.

This abandoned horse racing track was an exercise in hubris from its inception.

The final resting place of the businessman-turned-astronomer who helped discover Pluto stands near his observatory.

Although now a decaying ruin, this stone cabin's history includes several notable figures.

This 40-room dwelling tucked within a cliff was built by the basin's prehistoric residents.

This isolated outpost was once the only place to cross the Colorado River for hundreds of miles.