A lone cannonball remains lodged in the walls of the Hotel de Sens as a sober reminder of a revolution.

Mexico's astounding mummy museum with "the world's smallest mummy."

The stoutest tree in the world.

Frida Kahlo's childhood home, now a museum of her life and works.

66,000 pieces of art, donated by one of the world's richest men.

A scientific repository of goiters, boils and other ailments throughout Mexican history.

Diego Rivera's massive tiled fountain and failed infrastructure project.

Hear the quietest sound from across the dome.

Commonly acknowledged as the only public monument to the Devil himself.

An 18th century wonder of the world, lost in WWII, re-created at the Catherine Palace.

Stalin's march toward a more modern USSR flooded a monastery, leaving a unique and extravagant nautical marker, "The Flooded Belfry."

Museum celebrating the achievements of the Soviet space program.

Gargantuan home of Russian science.

Moscow's most popular cemetery includes the graves of numerous cosmonauts.

Stalinist skyscraper built with help of cryotechnology.

The tallest hotel in Europe.

This building holds the embalmed remains of the leader of the Bolshevik Revolution.

World's largest bell sits on the grounds of the Kremlin in Moscow.

The blood-soaked ruins of the castle where the murderous Blood Countess was walled in alive.

Synagogue built from the stones of Solomon's temple contains the golem of Prague.

Macabre astrological automaton clock dating to the late 1400s.

The only castle in North America to ever house European sovereigns.