The prototype for all Nazi concentration camps.

The world's tallest church tower reveals a spectacular view to anyone up to the task of climbing the daunting staircase.

This abandoned coliseum was intended to be a grand Nazi rallying ground before it was halted at the end of the war.

A small but immensely extravagant palace built by the "Night King."

A striking 12th-century-style castle built on the edge of a cliff.

A celebration of capitalism in Midtown.

A church that bred legends, and served as an inspiration for the Da Vinci Code.

Architectureal fantasy quarter of Rome.

The celebrated eyesore created by starry-eyed sweethearts.

The largest free-standing aquarium in the world resides in a hotel lobby in Berlin.

Standing in a state of "arrested decay," this ghost town allows for a detailed peek into Gold Rush life in an unusually harsh climate.

A horde of stray cats rule in this secluded Parisian cemetery under a bridge.

A pedestrian island in the middle of world-famous Times Square emits a strange (and purposeful) humming noise.

Paris' linguistic guide to the international language of, yes, love.

Whisper secrets in a busy station only to be heard on the other side of this acoustic arch.

The largest hot spring in the United States is, as the name suggests, a stunning show of natural color.

Four glass boxes hover over 1,000 feet in the air to give visitors an unparalleled view of Chicago.

Pompeii's less famous neighbor is still revealing her secrets.

France's most famous cemetery, with some of its most curious tombs.

The first declared National Monument in the United States.

Collapsing castle on the Hudson river was once the storage site of military surplus business.

Elevated freight railway turned wildly successful urban park.

Macabre astrological automaton clock dating to the late 1400s.

Famously misunderstood wonder of the ancient world