A modern-day Lascaux cave underneath Paris.

Of the many chalices in the running for the Holy Grail, this one in Valencia Cathedral sure looks the part.

This amazing example of Valencian Art Nouveau looks more like a cathedral than a public market.

This house's itty bitty size means no humans allowed.

A bizarre house filled with an astounding array of collections.

Amidst medieval and baroque buildings, five human-sized gherkins stand tall.

Six ravens are kept captive (but well-fed) at the Tower of London to prevent the fall of the Crown.

A 1,215-foot tunnel transports pedestrians beneath the River Thames.

The popularity of Sherlock Holmes led to the creation of his fictional address, turning the orderly London street numbers askew.

This memorial to the victims of the Romanian Revolution of 1989 is often compared to a potato on a skewer.

This communist behemoth is the heaviest building in the world and a legacy of a brutal regime.

Nearly three decades since the fall of the Soviet Union, the hero of the USSR still stands over Belarus.

Remnants of the city's Soviet history hover over this modern fast-food outlet.

An abandoned masterpiece of Soviet Brutalist architecture.

A small marionette collection located within the dark cellars of an 11th-century Austrian castle.

The slender brass strip in Prague's Old Town Square was used to tell time from 1652 to 1918.

A series of playful yellow penguins share a serious message about the environment.

The palace window through which Protestant nobles flung two Catholic regents, thus sparking the Thirty Years' War.

A turn of the century building boasting some of the most beautiful art nouveau architecture in Prague.

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

This tipsy office building in downtown Prague was originally called “Fred and Ginger.”

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

Two stunning 17th-century libraries and a cabinet of curiosities.

Macabre astrological automaton clock dating to the late 1400s.