This curious, round temple is the oldest still-standing marble building in Rome.

The only remaining arch of the oldest stone bridge in Rome stands in the middle of the Tiber.

In the early Roman Empire, people deemed traitors and criminals were tossed to their deaths from this rock.

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

A detailed pachyderm supports Rome's smallest Egyptian obelisk.

This large, circular tomb is the final resting place of the first emperor of Rome.

A master of trompe-l'oeil creates a stunning, tourist-fooling dome out of a flat ceiling.

A magnificent waterfall nestled in the heart of the El Yunque National Forest.

This former sugarcane transport tunnel is now a portal to a lovely beach.

An ode to one of the first concerts broadcast via satellite.

At the center of this cemetery stands a 2,000-year-old burial mound of the Adena culture.

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.

It took more than 20 years and a sharp eye for one man to assemble this quirky collection.

A floating museum that was sunk by a flood and left to rot in the tides.

What was meant to be a temporary exhibit is now a permanent fixture at the St. Louis Zoo filled with beautiful birds.

The Old Courthouse takes visitors on a captivating trip through St. Louis' timeline.

What was once a presidential estate is now an exotic menagerie and home to the Budweiser Clydesdales.

Less a museum than a bizarre fantasy world created by artists and engineers.

One of the few surviving examples of the first lock and dam system built on the Ohio River.

The largest ancient burial mound in Ohio.

Featuring one of the most complete and original collections of Presidential memorabilia, this is the site of the last front porch presidential campaigns.

The body of one of the world's most famous outlaws is covered in cement and iron to prevent it from being stolen.

A chapel built by Italian POWs during World War II tells a forgotten tale of the war on the home front.