This public space is speckled with the eerie remnants of a defunct amusement park.

This quarter-mile tunnel under the Bluff in Pittsburgh bends at a 45-degree angle.

Oldest building in California still in use.

Concrete strongholds stand guard over the Golden Gate.

Dedicated to the art and science of glass in equal measure, this space is as much laboratory as museum.

The Pennsylvania landscape depicted by a quarter mile of mosaics made from used road signs.

Quite simply the largest tree in the world (by volume).

An American flag was erected for every day that passed during the Iranian Hostage Crisis.

The land is home to swimming ponies and a legendary 18th-century treasure.

Fresh wooden posts have been added to ancient holes to recreate a primitive henge clock.

Once one of the world's great cities, Cahokia was a place of religious worship, trade and mass human sacrifice before being mysteriously abandoned.

The magic's in the hole!

One day a year it is legal to jump off of this astoundingly tall bridge that spans an Appalachian gorge.

The flower-shaped temple in Virginia aims to transcend the boundaries of the world’s religions.

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

Nothing says indulgence like a 1,500-pound chocolate castle.

Sections of the iconic limestone columns have been left uncleaned as a reminder of the city's polluted past.

The largest clock face in the United States is twice the size of Big Ben and infinitely more ad-sponsored.

The residents of the Neighborhood of Make-Believe live without much fanfare within the Pittsburgh Children's Museum.

A stone arch leads to a cavernous 1930s spring house tucked away in the Pennsylvania woods.

This historic Pittsburgh tennis complex is a rare example of natural red clay courts.

Color-coded signs direct drivers on a network of routes designed to avoid Pittsburgh traffic.

Meet your friends, marry your true love, or tell your enemies to kiss your butt under this historic Pittsburgh timepiece.

This restaurant offers a side of antiques, curios, and a bathroom chock full of owls.