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

San Francisco's oldest surviving monument and meeting place for 1906 survivors.

A library built during San Francisco's pioneer times is a student's retreat, bibliophile's sanctuary, and chess player's delight.

An office built to look like a giant basket.

This might just be the TARDIS of bookstores.

The gorgeous library at Trinity College is home to remarkable treasures of Irish identity.

Recognized the world over as the home of the McCallisters in the 1990 movie "Home Alone."

A place to eat for on-the-run agents and espionage enthusiasts.

Minnesota's oldest and deepest mine is now an underground physics laboratory.

This picturesque cliffside beacon no longer calls to sailors but shines once a year in honor of a famous shipwreck.

This turn of the century masterpiece has a mysterious goaty interloper.

In all of the 29 years it was in operation, no prisoners ever escaped successfully... or so they claim.

The oldest continuously operating church in California.

A peculiar mansion built by the troubled heir to the Winchester Rifle Company fortune.

This 1,300 year old monastery built atop a single rock was once only accessible depending on the whims of the tide.

Enormous statue of the Emperor of the Mongols.

A huge communist-era propaganda monument and mural that offers stunning views of the Mongolian capital.

This sprawling mini-golf empire is an impressive testament to a disappearing attraction.

At Chicago's revered Field Museum, visitors are invited to learn about and literally explore DNA.

At 207 feet, one of the world's longest continuous escalators.

This massive stained-glass masterpiece is thought to be the largest Tiffany dome in existence.

The twin towers in this Chicago fountain use 50 foot tall video screens to spit on people.

Four bald cypress trees in Lafayette Square, across from the White House, mark the southern edge of a 100,000 year old cypress swamp.

A former major munitions plant that has been converted into a sprawling art space.