The ruins of the largest gladiatorial school in Rome are largely hidden under modern streets.

This ancient market is often referred to as the oldest shopping mall in the world.

These unique markers designate the route American forces took during the Liberation of France.

You can spot this teeny tiny stained-glass window from the Bonifacius bridge.

The compass on its front was a handy tool for 17th-century merchants who needed to know the direction of the wind.

The bronzed skull of a beheaded traitor was affixed to the city gate in the 17th century.

Dedicated to the American general whose reply to a German demand for surrender was simply "Nuts!"

This elaborate towering structure was once famed for its revolutionary height.

An enigmatic monument to the Irish revolutionary who plotted an uprising against British rule.

This statue celebrating everyday life in Dublin has a few unsavory nicknames.

Experience what life was like in Ireland during the Viking and medieval ages.

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

The "lovely red Vega" of the legendary record-settling pilot.

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

A haunting tribute to pioneering photographer Clover Adams.

The actual model from the original "Star Trek" series is now on display at the National Air and Space Museum.

The walls of the iconic dome are hollow and have a secret stairway.

Home to items never before seen by the public.

The enchanting archway is the only surviving portal into Dublin’s lost medieval wall.

A museum that cashes in on its infamous little people while teaching you a thing or two about the Irish fey.

The gorgeous library at Trinity College is home to remarkable treasures of Irish identity.

A road that ends in the middle of a farmer’s field is one of the only remnants of this once-famous racetrack.

A neo-gothic statue modeled on German Emperor Kaiser Wilhelm II, which had its distinctive mustache shaved off by Nazis in World War II.

This historic covered bridge contains a series of macabre paintings that communicate one thing: everyone dies.