A morbid secret lies hidden within the beautiful walls of the Boston Athenaeum.

A toxic ghost town sitting atop a massive coal fire.

One of Philadelphia's largest murals resides hidden under this bridge.

This once rural mansion now sits in the heart of the city.

A meow-velous tribute to a beloved street cat, made famous on the internet.

One of the largest wooden constructions in Europe was meant to be a casino, but soon became an orphanage.

Large miniature theme park with 100-plus models.

This eatery re-creates dishes from the Ottoman Empire so you can dine like a sultan.

A small etching on the white marble parapet was written in runic script by a Viking mercenary.

A marvel of Byzantine engineering under the streets of Istanbul.

The world's only three-story rotary jail is now a museum to a bizarre trend in prison design.

A half-mile long and three stories high, this bridge over the Des Moines River Valley mimics a descent into a mine shaft.

The show pony of cave systems, Fantastic Caverns manages to live up to its name.

This mosaic-covered bar is brimming with curated curios.

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

Underground tunnels remain beneath this abandoned mental asylum.

A collection of haunted artifacts chronicles the career of the world's most famous paranormal investigators.

Connecticut grave of the woman responsible for the Winchester Mystery House in California.

The intriguing personal collection of a professional demon-chaser.

For two weeks every June, fireflies in the Smoky Mountains perform an astonishing light show.

This wondrous hideaway is suspended in a bamboo forest above a sanctuary for rescued llamas and alpacas.

Coca Cola may be "the real thing" but its inventor, buried at this Georgia gravesite, called it a "valuable brain tonic."

Tucked away inside a historic Savannah hotel is a hundred-year history presented in ladies' lids.

Where school buses go to die and be reborn as whimsical works of art.