Made of giant chains and hung with shackles, this iron cross honors those unknowns who perished under American slavery.

The Metropolitan Police refurbished the blue box (perhaps not coincidentally) the same year "Doctor Who" returned to TV screens.

This elegant arc of a waterfall marks a religious turning point.

An earthwork sculpture built by Robert Smithson in the Great Salt Lake only reemerges during drought.

During the holidays, a vintage subway train whisks New Yorkers back in time.

This mesmerizingly colorful pond looks like a scene straight out of a fairytale.

These Great Lakes sea caves accessible by boat in the summer turn into temples of ice reachable by foot in the winter.

Thanks to modern navigational tools we now know that the true prime meridian runs through a park next door.

Iceland's "Smoky Valley" is a beautiful river that is shrouded in a constant cover of steam clouds.

Abandoned power station once home to a squatter community, now being developed into an arts center.

Ralph Waldo Emerson spent two years living here decades before it became a Frederick Law Olmsted-designed park.

Abandoned concert venue legendary for its rock counterculture.

This sculpture by artist Fritz Keonig survived the 9/11 attacks and now stands as a monument to the victims.

The world's largest mountain carving could fit all of Mount Rushmore inside it many times over.

This modern monument to pagan belief looks like it was transported straight from ancient times.

A secretive collection featuring objects that were designed specifically for U.S. intelligence operations.

A stunning, abandoned limestone quarry in southern Indiana provided the stone to erect the Empire State Building.

Nestled in the heart of San Francisco’s bustling Financial District stands a unique homage to the Mayan and Beaux Arts.

California's own medieval Italian castle, authentic down to the 300-year-old iron maiden in the dungeon.

No matter what it might seem like on film, most scenes filmed on a plane are filmed at this LA studio.

A band of aerialists and circus performers putting on incredible shows in East Williamsburg.

One of the most scenic falls in Massachusetts has a history of death and grim legend.

Even Henry David Thoreau found this glacial pothole irresistible.

One of the steepest streets in the United States makes an intriguing challenge for cyclists.