Under a glass sidewalk lie the remains of some of Manhattan's oldest buildings.

The first declared National Monument in the United States.

Coins and medals straight from the mint await visitors to this shop in the nation's capital.

A 1,100-ton train fell through the floor in 1953. Workers got it patched up in just 72 hours.

An atomic bomb-proof strongbox protects the U.S. Constitution from terrorists and thieves.

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

Speak to a companion on the other side of the room loud and clear through this architectural anomaly.

A picturesque (all-natural!) beach in a landlocked state.

While most of the games in this arcade take quarters, that would have been a small fortune when they were made.

These faux-cliff dwellings allow visitors to climb around on a replica archaeological site.

View Kentucky's beauty and history from the perspective of painter John James Audubon, author and illustrator.

Home to a collection of artifacts and specimens from one of the world's preeminent geologists

A section of the long chain that blocked enemy ships from entering Constantinople.

The only Roman honorific column in Istanbul.

Taking the subway here means doing so over a bridge located in the middle of an estuary.

Have tea in a cemetery with a dazzling view of Istanbul.

Climb a set of vertiginous stone steps to the top of this impressive ancient edifice.

This former Imperial summer home was the venue for a royal slap that once echoed 'round the world.

This column celebrates Rome's victory over the Goths, and may be the oldest Roman monument in Istanbul.

Ancient serpentine sacrifice holder that has stood the test of time.

A fountain standing as a testament to a doomed alliance.

This half-forgotten fortress was constructed by the Ottoman conqueror of Constantinople.

A gorgeous, Gaudí-esque stairway constructed in the city of Istanbul by a prominent Jewish family.

A sixth-century Byzantine cistern hidden below a modern carpet store.