The highest paved road in North America winds its way up Mount Blue Sky in Colorado to an altitude of 14,130 feet above sea level.

When ecosystems collide in the arid Southwest.

The highest bridge in America was built for an almost unnervingly small amount of money.

The largest self-built castle in the U.S., six decades in the making.

A breathtaking array of ancient Pueblo structures and artifacts counterintuitively preserved by neglect.

The ancient dwellings of the Puebloans, located in the cliffs of majestic mesas.

This spectacular track has run continuously since 1882.

A graveyard for early settlers, sometimes called Old Pioneer Cemetery, hidden in the woods on a hillside.

An obscure waterfall that looks like something out of a fantasy novel.

The tiny church offers succor to travelers driving by, but only eight at a time.

Cave carved out of a huge snow drift collapsed killing one and injuring five in July 2015.

A French chateau, failed utopian community, odd museum, and Stonehenge replica in rural Washington State.

An extraordinary mixture of natural beauty and man-made phenomena.

This long, dark tunnel is open to hikers, but those without lights are known to get confused even on the straight path.

A fine, large-aperture telescope available for public use.

The second tallest railway trestle bridge in America.

This tree has witnessed nearly 1,000 years of history.

At the most northwestern point of the contiguous United States lies a trail leading through an ancient forest to stunning cliff-side vistas and massive oceanside caves.

This playground sculpture of an icon from the past is dedicated to the children of the future.

A tribute to the Nirvana frontman hides beneath the bridge that was the singer's beloved hangout spot.

From overly ambitious (and eventually abandoned) atomic dream to bustling office park.

This bridge provides safe passage for squirrels.

This famous bridge twisted itself into oblivion, but not for the reason you might think.

An abandoned network of military bunkers and tunnels open for anyone willing to descend into the darkness.