The only fully-realized skyscraper built by the famed American architect, Frank Lloyd Wright.

Once the smallest park in the national system.

It reportedly took three years to sort through all the objects in this eclectic lifelong collection.

This abandoned, windowless concrete block is one of the strangest buildings in Tulsa.

Nature's biggest mammal swims in landlocked Oklahoma.

Mysterious stone tower featured in many alternative histories of the New World.

A miniature city within a city, complete with traffic signs, signals, and streets to teach Baltimore's youth traffic safety laws.

The most powerful waterfall in all of Europe.

A look into the Church of Scientology's deeply unfavorable view of psychiatry.

Remants of foundations, streets, and streetcar tracks inhabit the cliffs where a landslide occurred in 1929.

The Denver airport is guarded by a 32-foot-tall sculpture of a demonic horse.

A peaceful place in the woods where everything is a work in progress.

This sky-high radio mast is formerly the tallest man-made structure in the world.

The site of the one of the most deadly train wrecks in American history.

The small cave that housed Tennessee's "first citizen."

The former Willingdon Airport started operations in 1929, in India's capital, Delhi. Now, it's used for maintenance runs and helicopter rides.

A Zoroastrian funerary tower where excarnation rituals are carried out is threatened by the area's dwindling vulture population.

This weekly bazaar started in the 1960s as a way for hippie travelers to barter their goods.

This 17th-century mausoleum is topped with an acoustic marvel.

Deep in the Thar desert, a temple crawling with thousands of holy rats.

A nearly unconquerable island-fort in the Indian Ocean.

Temples adorned with intricate, erotic sculptures make up one of the "seven wonders" of India.

An extraordinary "City of Caves" carved from solid stone.

Da Vinci's equestrian statue, 500 years in the making.