Ancient Egyptian wigs, South American feather headdresses, a bounty of anthropological artifacts in Oxford.

This macabre masterpiece of a mural is one of Francisco Goya's "Black Paintings."

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

Bubbling up from deep underground is the warm crystal clear water that fills the Warm Springs Pools, America's oldest spa.

One of Antoni Gaudí’s earliest buildings, built between 1886 and 1890 for the industrialist Eusebi Güell.

A beautiful but toxic fountain of mercury.

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

The 2,000-year-old Roman columns are hidden within Barcelona's Gothic Quarter.

The largest Art Nouveau complex in the world is a Barcelona hospital with a 600-year-long history.

These secluded and abandoned anti-aircraft defenses have become one the most scenic viewpoints in Barcelona.

This semi-secret storybook hedge maze is also the oldest garden in the city.

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

Forget Hollywood, one of the biggest stars in the world can be found in Roanoke, Virginia.

A focal point of in Denver’s skyline for over a century, inspired by a Venetian basilica.

The burial grounds of a secret society includes fences topped with fake Tesla balls.

The oddly shaped, steam-spewing building is now an art studio and gallery.

A sacred site for Native Americans surveyed by George Washington and owned by both King George III and Thomas Jefferson.

This campus chapel is Robert E. Lee's final resting place and a topic of debate about the legacy of the Civil War.

A working cattle ranch with remarkably well-preserved prehistoric petroglyphs and ancient ruins.

The second-largest cave chamber in the world was discovered in 1898 by a 16-year-old and a friend known as "Pothead."

A popular rock that acted as a waymarker for American pioneers.

This Yellowstone geyser may not shoot as high as the nearby Old Faithful, but it erupts for considerably longer.

One of nature's most well-scheduled phenomenons resides in Wyoming's Yellowstone National Park.

The largest hot spring in the United States is, as the name suggests, a stunning show of natural color.