Millions of numbers carved in glass represent the tattoos forced upon victims.

This area was once known for being a lawless haven for rough-and-tumble sailors, earning the maritime-themed nickname "the black sea."

An easy-to-miss garden in Boston's North End honors the mother of JFK and others who lost children in WWII.

One of the last remaining World War II Victory Gardens in the U.S. is quietly growing across from Fenway Park.

Mrs. Mallard and her brood are a beloved fixture in Boston Public Garden.

The tomb of Increase Mather and his son Cotton, influential colonial ministers obsessed with the occult.

Berthed at the Charlestown Navy Yard in Boston, "Old Ironsides" is the oldest commissioned warship still afloat.

One of the now-less-hidden floral gems of the "Emerald Necklace."

One of the oldest used bookstores in the U.S. has been selling antiquarian treasures since 1825.

America's original house of worship for Spiritualism, the religious movement based on communing with the dead.

These sacred Mesoamerican ruins feature peculiar petroglyphs hidden in the stones.

These barriers stand as stark reminders of Northern Ireland's troubled past.

It was once nicknamed "the most bombed hotel in Europe."

This neon landmark has been posing this deadpan question to follicly-challenged Dubliners for over 50 years.

The 19th-century pharmacy (now a used bookstore) was featured in James Joyce’s "Ulysses," and has changed very little to this day.

One of Ireland's most infamous prisons for rebels including men, women and children.

The gorgeous library at Trinity College is home to remarkable treasures of Irish identity.

The iconic boulevard is the perfect place to catch sight of a bicycling skeleton, a levitating Satan, or a chef with his head stuck in a pizza.

A vista of the city and sea from atop the little-known viewing deck on an unassuming Columbus statue.

Gaudí's famously flamboyant architectural style is on full display in this sprawling park and garden.

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

One of the few remaining ancient aqueducts described by Frontinus as 'the most solemn testimony of the Empire.'

If you can look past the nearby sewer pipes, this urban sinkhole grotto is a mini-paradise.