Friction between grains of sand cause a curious "singing" sound.

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

Perfectly preserved ancient monastery in an impossibly dramatic location on a rocky island in the Atlantic.

A remarkably intact castle that once was the largest in Ireland.

The final resting place of the great navigator, or maybe his brother.

This amazing example of Valencian Art Nouveau looks more like a cathedral than a public market.

Of the many chalices in the running for the Holy Grail, this one in Valencia Cathedral sure looks the part.

Legends surround this natural rock formation that looks like a Moorish king wearing a crown.

This magnificent market stands as a poignant symbol of the suffering caused by the Spanish Civil War.

An unusually designed bridge from the 1920s was built to withstand the tides and winds of Maine.

Once the largest public hospital for the mentally ill was also surrounded by controversy.

This city square dates back to the Scottish Enlightenment and was home to some of Scotland's brightest minds.

Edinburgh's oldest statue hides within a parking lot behind the city's iconic cathedral.

The tomb of one of Scotland's bloody historic villains is a magnet for bumbling desecrators.

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

Overlooked by many, the two famous Scottish warriors guard the main gate of Edinburgh Castle.

This ancient Visigothic church might hide an ancient treasure.

The fragmented remains of a massive public bath connected to the city's water supply.

The ruins of an ancient stadium that hosted gripping chariot and horse races.

For decades, Puerta del Sol has been illuminated by a giant, guitar-wielding bottle of sherry.

Though tiki culture has gone in and out of fashion, the Tonga Hut has always been flying the flag in Los Angeles.

Established in the '60s, a family-owned tropical drink bar founded by Ray Buhen, bartender to the stars.

This tower commemorates the spot where George Washington hoisted the Grand Union flag.

Run by a eugenics advocate, this aging institution conducted secret radiation experiments sponsored by Quaker Oats.