Once an opulent Art Nouveau hotspot, the Constanța Casino is one of Romania's most beautiful abandoned buildings.

17th century mosque for Shah Abbas' harem.

Remnants of successive wars and Muslim colonialism in the 11th century.

An abused and forgotten metropolis, abandoned for centuries.

Futuristic apartment blocks are the backdrop for Montreal surfers hangin' ten on the Habitat '67 standing wave.

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

An abandoned saucer-shaped monument in the Bulgarian mountains.

A castle perched precariously over the Crimean Sea.

Unusual building appears to be haphazardly built from randomly piled bricks.

A museum glorifying the life of Stalin, located in the city of his birth.

The most alien-looking place on Earth.

These Nubian pyramids are strange and unique, even by pyramid standards.

The most remote tree in the world survived desertification, but not a drunk truck driver.

The world's most remote memorial to the victims of the UTA Flight 772 disaster.

The world's highest and most dangerous infinity pool lies at the precipice of Victoria Falls.

The remains of diamond fever taken over by the desert.

This "dead marsh" sits among the largest sand dunes in the world, a forest frozen in time.

Submerged trees jut ghost-like out of an idyllic turquoise mountain lake.

Church built on the site where the last tsar of Russia and his family were killed.

Monastery complex at the location where bodies of the executed Romanov royal family were discovered.

Siberian ghost town built by gulag prisoners.

A huge communist-era propaganda monument and mural that offers stunning views of the Mongolian capital.

A remote forest of stone pillars along the Lena river.

This beautiful natural train tunnel is said to grant the wishes of visiting lovebirds.