This mysterious artificial cave has long puzzled New Englanders.

The remnants of a Gilded Age elegance preserved in the middle of a stark modern tower.

This historic patch of real estate offers a glimpse of colonial Boston.

A morbid secret lies hidden within the beautiful walls of the Boston Athenaeum.

A tiny plaque marks the location of the water source that facilitated the birth of modern-day Boston.

A plaque memorializes the Boston location of one of the largest nightclub fires in history.

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

Site of a famous 19th-century transcendentalist utopian community, now abandoned.

The strikingly modern structure stands out among the brick buildings speckling the Harvard Business School's campus.

A secret door leads to this cozy dive that sells only “milk.”

Hidden on a cobblestone street in Glasgow, a Czech Cajovna-inspired teahouse serves as a hangout for Bohemians.

"Respectful to the dead, safe and sanitary to the living, dedicated to the Genius of Memory..."

This obscure walkway links Edinburgh’s Old Town with one of the city's prime vantage points.

A beautiful Greco-Roman structure houses a well once believed to have healing powers.

A secret garden in a picturesque Edinburgh village has inspired artists for centuries.

One of Edinburgh's oldest pubs hides a 19th-century skittles alley in the back.

This historic pub has maintained much of its 1906 decor, including a small sequestered room for women, where orders were slipped through a tiny window.

A 18th century graveyard and its astonishing cortege of macabre iconography.

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

Ruined 11th century abbey built by King David I in Edinburgh, Scotland.

360° views of the city plus five floors of optical illusions and hands-on science.

The unedited photograph called "Bliss" has graced the screens of over a billion computers.

This nonsensical smiling boat shuttles passengers between two places they could've easily walked between.

The island home of an unlucky whaling captain whose story inspired a great American novel.