A hospital where antique dolls are given new life.

This small church was constructed over the ruins of three temples dating to the Roman Republic.

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

A mysterious chasm in the heart of the ancient Roman Forum, the Lacus Curtius was once believed to be a gateway to hell.

This ancient market is often referred to as the oldest shopping mall in the world.

A Hawaiian stairway to heaven—that you can't climb.

Hidden behind a YMCA stands the remains of a ceremonial site that dates back hundreds of years, whose ground is still considered sacred to many Hawaiians.

These falls, sometimes called the "Niagara of the West," still put on a good show at the right time of year.

The decaying ruins of a failed mining company’s water diversion project cling to the side of a desert canyon.

These huge stone ovens in the desert fueled the Nevada silver boom, and may have also been a hideout for outlaws.

A dark, dank room in subterranean Manhattan was the site of a ghastly murder.

The ruins of an abandoned church mingle with the graves at Oaxaca’s General Cemetery.

The abandoned husk of a mental institution that failed to save a Jazz Age icon still sits nearly unchanged.

The Brigadier General was so afraid of being buried alive that he had a buzzer installed in his mausoleum, just in case he woke up.

Collapsing castle on the Hudson river was once the storage site of military surplus business.

A jaw-dropping "megalibrary" that turns book-browsing into a geometric adventure.

History is on display in this hall, which has served as the seat of city government for centuries.

Underneath the historic center of Mexico City, the remains of a temple dedicated to the Aztec god of the wind.

This foreboding building was the headquarters of the terrifying Spanish Inquisition in Mexico.

This "City of Books" holds a museum, library, and the complete personal book collections of five of Mexico's greatest thinkers.

Psychedelic murals coat the inside of a nondescript research library.

The burial place of some of Mexico's most prominent residents is full of macabre stories and hidden masonic symbols.

Gilded heaven for philatelists and architecture freaks, still in full working order despite sitting atop tremulous ground.

A Volkswagen Beetle decorated with millions of beads connects Mexico's past and future.