The only National Monument ever to go missing for nearly 50 years then resurface in a dump.

A clone of a cloned tree that was so important it allegedly had its own guards.

This elaborate towering structure was once famed for its revolutionary height.

A super-sized promotional trick that is now a D.C. landmark.

The country's oldest continually-operated mini golf course lies hidden in plain sight, eclipsed by one of D.C.'s most popular tourist attractions.

The internal railway of one of the biggest steel plants in America has been transformed into a linear park with unique industrial views.

The longest escalator in the Western Hemisphere takes over three minutes to ride down.

Three columns of volcanic rock shoot out of the ocean.

This stunning concert hall has become a symbol of Iceland's national recovery.

This tiny museum's sizable collection is jammed into a former underground public toilet.

An encyclopedic collection of mammal penises.

One of the tallest buildings in Iceland, and perhaps, the most visually impressive.

Medicinal spa created with the discharge from a geothermal energy plant.

Equal parts record-breaking temple to consumerism and bizarre fun park, it's more than you think it is...

The U.S. Fish Commission’s effort to mass produce carp.

The bank that helped fund the Mexican-American War and the purchase of Alaska met its downfall after helping Augusto Pinochet launder money.

On the Fourth of July this area will transform into a Pompeii-like storm of falling embers and ash.

The 5.5-mile ring of steel posts around the Capitol Building is one of the largest (and most uniform) of its kind in the world.

An ear-piercing buzzer calls lawmakers to a vote with a series of long and short rings to form coded messages.

Corn-inthian columns with a uniquely American take on neoclassical architecture.

A muscular Art Deco monument represents the struggle between regulators and unbridled markets.

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

Disks are rolled out onto the south lawn to absorb the impact of Marine One's wheels like giant coffee coasters.

Obscure Freemasons still live in D.C.’s largest private residence.