A tiny mosque decorated with mosaics using an early form of recycling.

The untimely death of a dignitary's daughter led to this fort being abandoned before it was ever finished.

This colorful palace is an oasis of calm amid the hustle and bustle of the Buriganga riverfront.

All that is left of an Armenian community that thrived in Dhaka 200 years ago.

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

The first Russian Orthodox church in North America and an Alaskan landmark.

Around 100,000 bodies are buried below the medieval headstones, many of which mark graves with multiple bodies stacked up to 12 deep.

Macabre astrological automaton clock dating to the late 1400s.

St. Mary's features one of the most spectacularly decorated cathedral interiors in all of Europe.

A floundering Polish shipyard was once the soul of the Solidarity movement that capsized communism.

This sprawling concrete suburb of Kraków was designed by the Soviet Union as the model proletarian city.

The former Nazi concentration camp stands as a museum to remember this dark chapter in European history.

This iconic Parisian bookstore doubles as the "Tumbleweed Hotel" for traveling writers.

Founded in 670, this ancient mosque is an architectural time portal.

340-foot statue built to honour the Heroes of the Soviet Union.

The largest catacomb system in the world.

Legend says if you stick your thumb in the hole and it gets wet your wish will be granted.

The ancient latrines of the Greeks, in all their public glory.

Five sultans and their families rest in eternal splendor, teeming with overlooked beauty and drama.

A marvel of Byzantine engineering under the streets of Istanbul.

In this historic region, homes and churches are carved into ancient volcanic rock formations.

America's post-nuclear-attack chambers of Congress.

The site of Paul Revere's historic two lantern warning.

The marker offers a rare chance to be in four U.S. states at once, though there's some controversy over its geographic accuracy.