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

The house where John Wilkes Booth conspired with his co-conspirators.

A rotating cast of guys and dolls in front of a Washington, D.C. building.

When it opened during the final years of the embargo, all the drinks and cigars were free.

The most decorated dog of World War I is preserved in the Smithsonian.

The beloved statue at the National Academy of Sciences is oh so inviting to sit on.

This lonely waterfront memorial to the men of the Titanic was erected by the "Women of America."

The country's oldest continually-operated mini golf course lies hidden in plain sight, eclipsed by one of D.C.'s most popular tourist attractions.

A painfully obvious spy house sits right across the street from the Russian Embassy.

A monument in Washington D.C. marks the spot from which all other roads were supposed to stem.

There's a 12-foot-tall replica of the Washington Monument hidden under a manhole nearby.

Enormous piles of historically significant stones, dumped by Congress in a forest, and abandoned for 60 years.

Go deep down into the earth to experience the world of Welsh coal miners.

The enormous earthwork sculpture honors the ponies that lived and worked in the old colliery.

A beautiful but toxic fountain of mercury.

For those with no fear of heights: a skywalk 4,700 feet up on a Chinese mountain.

The secluded site of a 1943 plane crash and amazing rescue is only accessible by hiking through the woods.

An artist's mausoleum with a haunting echo.

The painter of "The Scream" is laid to rest under a stoic bust of himself in the humble corner of an Oslo cemetery.

Oslo's historic toboggan run has been letting thrill seekers slide from train stop to train stop for over a century.

Ruins of two abandoned stations destroyed by the power they sought to harness.

St George's Leprosy Museum depicts the gruesome afflictions of those suffering from the disease.

This Victorian-era public house has set the standard for pub-style elegance for over a hundred years.

An important landmark in the history of algebraic logic.