A tiny red pebble marks what may be the quietest outdoor spot in the United States.

This charmingly homemade amusement park has been growing for 40 years.

A 300-yard long natural tunnel runs through a ridge deep in the Appalachian Mountains.

This former tuberculosis research hospital endeavored to cure the dreaded disease with fresh air and positive attitudes.

Enormous piles of historically significant stones, dumped by Congress in a forest, and abandoned for 60 years.

A master of trompe-l'oeil creates a stunning, tourist-fooling dome out of a flat ceiling.

An abandoned relic of the city's failed experiment with below ground transit.

The eccentric mansion of one of the most popular horror authors of modern times.

The name of this famed hospital was once a byword for the horrors of medical and psychiatric care.

A particularly creepy abandoned hospital that sparks interest for lovers of the supernatural.

This community on a small Venetian island has taken to painting their houses in bright neon hues.

The longest navigable underground river in the United States is home to countless blind and albino animals.

This volcanic cave lake is essentially hard proof that Iceland is the most magical place on Earth.

A strange rock with a sinister reputation lurks within the crimson waters of this Scottish glen.

This road in the Great Smoky Mountains was supposed to assuage a displaced community, but ended up a $52 million dead end.

The oldest surviving bridge in New York City, which reopened to pedestrians in 2015.

A three-story copper skybridge connects two Manhattan buildings with Art Deco luxury.

A sculpture made of 10 Cadillacs as a monument to the "Golden Age" of the American automobile.

An enormous park-like oasis, full of famous Chicagoans' graves.

European castle ruins in an American state park are actually the product of death and grief.

A mysterious castle built as a monument to lost love.

This maze-like slot canyon is a unique gem within an already fascinating geological area.

Amazing and mysterious Neolithic settlement on Scotland's Orkney Islands.

Rare recess caves fill this unbelievably beautiful Ohio park.