Once a sewer culvert, this road tunnel now offers cyclists and pedestrians a subterranean stroll under the C&O Canal.

The span is crooked and made from two older recycled bridges.

This former train station was once an important shipping depot for the regions farmers.

Live data is transmitted from the Atlantic coast to instantly recreate the ocean waves in this fountain at the NOAA headquarters.

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

Fittingly, America's museum of architecture is itself a magnificently designed old building.

During the holidays, a vintage subway train whisks New Yorkers back in time.

This abandoned subway station beneath the Waldorf-Astoria hotel is allegedly used to secretly transport presidents.

One of the last mosaic tile facades found in the city.

Long-abandoned trolley tunnels just a mile away from the White House are turning into an art space.

An abandoned Gold Coast-era mansion once intended for the exiled ruler of Albania, who never arrived.

The ruins of this former mining boomtown once housed over 3,000 people. Now, the population is two.

Home of the International Space Hall of Fame.

The remains of Abó, Gran Quivera, and Qurai are monuments to the long, complicated history of the Indigenous people of the Southwest.

Huge otherworldly domed rocks on the shore of a deadly lake.

A huge musical sculpture and other art installations on the National Oceanic and Atmospheric Administration grounds.

Tour the original street level of Port Angeles, buried underground in 1914.

This dilapidated ship carcass covered in trees is a striking sight.

A surreal landscape where fanged rocks rise from the ground and the ocean feels like a great mystery.

A walk through the historic city center, under the streets of Seattle.

This natural marble cave is one of only five national monuments in Oregon.

With a crest near 10,000 feet, this treeless fault-block mountain in eastern Oregon provides stunning views and spectacular glacial landforms.

The victims of a free-floating Japanese bombing during WWII are remembered by this stone monument.

As a show of peace, a Japanese naval pilot gifted his 400-year-old Samurai sword to the Oregon town he bombed.