These bleak 800-year-old ruins were once the royal residence of choice for hunting in Sherwood Forest.

These medieval monastery ruins are surprisingly overlooked by most tourists.

The world's longest nonstop reversible cable car soars through spectacular scenery to the medieval Tatev Monastery.

What was once England's second-richest abbey is now a haunting ruin.

The undercroft is a spectacular example of medieval Cistercian architecture.

WWII artifacts, including the building itself.

Britain's tallest megalith towers over the cemetery of a quiet English village.

Enter the world under the hill at this ancient UK burial chamber.

This skeletal, unfinished Gothic church once housed a miraculous masterpiece by Raphael.

The industrial architecture honors the laborers who brought the Exposition Universelle of 1900 to life.

This tin chapel was built by POW's during World War II and is painted to look like something much more grand.

This Old West eatery along America's Loneliest Road was originally a stop on the Pony Express.

During the Industrial Revolution this “Temple of Invention” was full of intricate miniature machines and gadgets.

In the basement of the U.S. Capitol Building is a hidden storage room full of ornate floor tiles leftover from the 1850s.

One of the largest and oldest caravansaries in Persia.

A hidden gem on the lawn of the U.S. Capitol Building designed by landscape architect Frederick Law Olmsted.

Long before air conditioning, Persian architects found an ingenious way to cool off.

Please don’t anchor your boat onto the Department of Defense’s underwater data cables.

Built by the patriotic residents of Boonsboro in a single day.

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

A computer bug so primitive it was an actual insect.

The oldest building in the District of Columbia was preserved because of a mistaken connection to George Washington.

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

The monument's pointy aluminum tip has been melted down by repeated lightning strikes.