A little-known subterranean street runs under some of the best-known buildings in Chicago's River North.

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

Dyed by iron oxide over centuries, these sandstone rocks rise thousands of feet into the sky.

Stepping away from the glitz of mobsters and casinos to learn about the other history of Vegas.

Legend tells how a Spanish soldier disappeared from this isolated sentry box without a trace.

This chapel on a cliff is renowned for its healing powers and was founded on the site of a supposed divine intervention.

Cavernous opening completely encased in Karst limestone.

Send a postcard while vacationing with Satan.

The development of this cliffside waterpark is representative of Mexico's history of co-op tourism developments.

World War II-era bunkers are hidden under the beaches of this picturesque park, which is still scattered with wartime watchtowers.

Exquisite wall sculptures carved in secret by an early quarryman in an obscure corner of the Paris Catacombs.

This statue was given to France by the United States to commemorate the centennial of the French Revolution.

An "inside out" building in the historical center of Paris, featuring Europe’s largest modern art museum.

Paris' linguistic guide to the international language of, yes, love.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

Beirut's thinnest building was the result of feuding brothers.

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

Gaudí's famously flamboyant architectural style is on full display in this sprawling park and garden.

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

Step back in time at this 19th-century kiosk.

An unassuming music museum recounts the rags to riches story of a dramatic Portuguese genre.

Eat the ultimate iteration of Portugal's most beloved pastry.

Elaborately carved to showcase the glorious wealth that the age of exploration brought to the Portuguese empire.

This Industrial Age architectural and engineering gem helps visitors and residents alike traverse Lisbon, “The City of Seven Hills.”