This mysterious structure by the Washington Monument is a flood barrier designed to protect the White House against rising waters.

A derelict bit of infrastructure from the canal that once ran through D.C. is landlocked in the heart of the city.

An overlooked memorial honoring the local Washington residents who died in World War I.

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

This magnificent Cincinnati graveyard is also a popular public park.

Once damaged by Hurricane Agnes, this bridge is now on the National Register of Historic Places.

A piece of baseball history is preserved in a Pittsburgh parking lot.

The site of Neil Armstrong's first flight is marked by a full on replica of the moon landers.

This alley-cum-fan gallery in the ex-Nirvana drummer's hometown holds the world's largest drumsticks.

The oldest remaining authentic Putt-Putt course that Donald Clayton created in Ohio.

An old railroad grade built for the construction of Hoover Dam is now a recreational trail featuring several tunnels and sweeping views of Lake Mead.

These markers are used to document elevation changes around the famed dam.

These markers are used to determine the ground stability of the Strip.

A legendary tree towers within its own vibrant sanctuary.

A retrofuturistic art installation in the Pittsburgh Airport.

This historic house museum that celebrates one of the world's most influential social reformers is also one of the most haunted locations in Chicago.

This memorial plaque remembers a strangely shallow maritime disaster known as "Chicago's Titanic."

This alley in downtown Chicago held the bodies of over 600 people after the fateful Iroquois Theatre fire.

A gothic church spire sits atop this skyscraper, the tallest church in the world.

Dedicated to the victims of one of the deadliest hurricanes to strike the United States in recorded history.

The highest point in New Jersey is marked by a massive, if simply named, obelisk.

An abandoned railroad tunnel transformed into a creepy path for hikers and cyclists.

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

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