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

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

This quirky curiosity shop takes its cues from the world's bazaars.

This kitschy tavern is also home to rare early editions of "Treasure Island."

Catering to broken dolls for almost 200 years, this repair shop is now a charnel house of doll parts.

The Beaux-Arts aquarium boasts a vast collection of saltwater and freshwater fish on an island in the Detroit River.

This sprawling bookstore spans four floors and has more than a million books in stock.

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

This morbid, delightful curiosity shop offers everything from animal bones to human teeth.

An ancient passage filled with stalls selling used books, once frequented by Vincent Van Gogh.

A Dutch passageway's artistic, aquatic-themed makeover pays tribute to the capital city's famed waterways.

An eerie, protected forest of old-growth oak trees, many of which are now dead.

Popular river that runs through the remote Serbian municipality of Leskovac.

Religious perseverance and cultural coexistence manifest in an architectural gem that multiple wars couldn't topple.

For over 40 years, this quaint little house has teetered on a rock in the middle of a river.

A sinuous path among steep cliffs creates a stunning sight in southwestern Serbia.

Structure built from the skulls of vanquished foes.

This 14th century castle withstood years of battle but is now sliding off the hills into the Danube.

The site of many battles and tragedies, including the 40 maidens who leapt into the sea.

An abandoned saucer-shaped monument in the Bulgarian mountains.

Bizarrely shaped rock formations in northwest Bulgaria come with equally bizarre legends.

An architectural marvel that spans the Arda River, and has stories of a haunted past.

Festival of Perpetual Life and Rebirth.

An industrial site turned into Hungary's most cherished natural wonder.