These official units of measurement—including chains and perches—lie hidden beneath tourists' feet in a popular London hub.

The site of a defunct mill, that once supplied marble for the construction of the Lincoln Memorial.

It takes a nine-mile hike to reach these hot springs, but weary hikers are rewarded with stunning views and a warm soak.

Tropical paradise strewn with hundreds of World War II wrecks.

These ancient monoliths make up one of the largest archaeological sites in Palau.

Down the road from where the Wright brothers lifted off is another flight tribute practically hidden from sight in the woods.

This shifting North Carolina sand dune is an odd little desert surrounded by oceanic forest life.

Beautiful Gothic-inspired lighthouse stands out among the run-of-the-mill striped fare on Bodies Island.

Thanks to a quirk of elevation this gift shop produces magic doughnuts that are found nowhere else on Earth.

This super steep hike ascends 2,000 feet in less than a mile.

Strange red rock formations that have been attributed to a higher power for hundreds of years.

This volcano rises like a giant anthill from the plains below, with a road spiraling up to the rim.

An enormous public square and parade ground built to celebrate Ghana's independence.

The only Civil War battle in Washington D.C. took place near this highest natural point in the city.

Look closely and you’ll notice that the color changes a third of the way up the tower.

Those with a sharp eye can find the hidden image of a German Shepherd on the memorial's Mural Wall.

Public opinion is still divided on this enormous sculpture in front of Baltimore's Penn Station.

It's not hard to see why the historic Peabody Conservatory of Music's library has been described as a "cathedral of books."

The highest point in Delaware is located under a trailer so this marker across the street will have to do.

A former waterfront market is now in the center of town due to some interesting Boston engineering.

This mosaic dedicated to John Lennon was tended for years by a Beatles super-fan.

The last remaining relic of San Francisco's glittering 1915 Panama Pacific Exposition.

The miraculous hydrant that saved the Mission District in 1906.

San Francisco's newly reopened hands-on science museum.