A beautiful but toxic fountain of mercury.

This semi-secret storybook hedge maze is also the oldest garden in the city.

These gigantic skeletons tower over visitors and provide insight into the creatures that once ruled over Ireland.

An 80-year-old plane tree is devouring an iron bench at Ireland's oldest law school.

Commemorating the landing of William of Orange with his European army on their way to the Battle of the Boyne.

This former World War II torpedo testing location is now an important nesting site for migratory birds.

An abandoned shipping control tower looks like a satellite perched at the end of a pier.

A restored World War II Churchill Mark VII Tank now stands guard in Carrickfergus.

An unassuming tribute to engineer William Bald and the workers who built one of Europe's most scenic coastal roads.

400 million years of erosion shaped these fascinating seaside caves, which made an appearance on 'Game of Thrones.'

These engineering masterpieces are a dominant feature of the Belfast skyline.

These sculptures honor the knights who once called Carrickfergus Castle their stronghold.

Possibly the world's oldest rug, this Egyptian relic is woven entirely from ancient cat hair and once carried a mummified human foot.

Gutted airplanes slowly decay in a Florida field.

A trek through the solar system here on earth.

A sprawling maze of used books piled from floor to ceiling.

A winding path built in secret on the edge of the continent.

Thirteen trees representing the original thirteen colonies were planted with soil from historic Revolutionary battlefields.

A shining, cold, black organ lies in San Francisco's financial district.

Faceless white figures loom over the city from the rooftop.

Adolph Sutro's little-known, geographically inaccurate, deprecated monument.

Not merely a museum – but a whirring powerhouse that offers a subterranean peek into the heart and soul of cable car operations.

The stones that traveled from Spain to eventually become a holy place for San Francisco's nature worshippers.

An overlooked and unassuming engineering marvel.