This long line of cement defensive wedges is named after the famous chocolate bar for obvious reasons.

Medieval irrigation channels built into the sides of mountains provided Valais with water for hundreds of years.

For a brief time in 1960s France, families could climb into a tiny submarine and be pulled along an underwater journey.

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

One of the world's heaviest musical instruments towers within a popular urban park.

Walk in the footsteps of the gods and straddle two tectonic plates.

Venice's "Island of the Mad."

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

One of the oldest scientific gardens in Britain, containing more than 13,302 plant species in its core collection.

Surreal riveted sea forts once protected the Kent shores from German attack.

A island reachable by a causeway at low tide is possibly one of the earliest Western European locations to be identified in text.

The one-time watch house for incoming ships at the Golden Gate now stands abandoned and hidden in trees.

A museum of magic with a Sadist past.

The gloomy ruins that inspired Bram Stoker to bring Dracula to life.

Quite simply the largest tree in the world (by volume).

This eye-popping Icelandic crater lake is surrounded by red volcanic rock.

A mechanized clock where a man fights off a dragon, crab, and rooster.

A student driver's nightmare.

Hidden in an ordinary Midtown building is a one-room museum dedicated to the greatest escape artist.

Walk 2,300 feet above the ground on the "Troll's Tongue."

Walk upon the mementos of the dead in this Parisian courtyard paved with medieval tombstones.

Under a glass sidewalk lie the remains of some of Manhattan's oldest buildings.

This unmarked and unloved Manhattan subway grate created one of the most iconic images in American cinema.

Three bridges and one giant canyon make up this fantastic Spanish settlement.