These imposing walls and towers look more like the ruins of a fortress than a monastery.

A collection of housewares from recent Irish history adjoined by a tower from ancient Irish history.

The oldest inn in Kilkenny was established by the first convicted witch in Ireland.

This ancient Irish religious site is covered in ancient carvings, many of which have barely aged.

The last of Amsterdam's original sea level markers remaining in place.

One of Amsterdam's narrowest houses is located right across the canal from its widest.

In the days before house numbers, these colorful signs held clues about various buildings' purposes.

A public urinal so pretty, it was declared a national monument.

The last of Philadelphia's wood-paved streets is now a landmark of terrible engineering.

Golden and naked, the figure that was once the highest point in New York is all that remains of the second Madison Square Garden.

A tour de force of a fountain, memorializing a man who loved fountains more than anything else.

An Irish Memorial commemorating those who perished due to potato blight.

A daily replay of the experiment that proved the rotation of the Earth.

The sounds of the world's largest fully functioning pipe organ dazzle shoppers at a Philadelphia Macy's.

This little-known Revolutionary War fort is supposedly haunted by the ghosts of its past.

Current docking place of the SS United States, the fastest transatlantic ocean liner.

This elaborate towering structure was once famed for its revolutionary height.

Ant sculptures march up the side of what used to be an iconic spot in punk rock lore.

Yo, Adrian!

A clone-tree in Washington Square Park sprung from seeds that went to the Moon and back.

The first American department store, and home to the largest operating musical instrument in the world.

Dr Barnes' $25 billion private collection of art and arboretum.

This little-known collection holds everything from "Dracula" notes, to the manuscript of "Ulysses," to the forged works of Shakespeare.

This charming colonial alleyway is one of the oldest continuously used residential streets in the U.S.