A dismembered holy head stares out from her beautiful reliquary at the St. Dominic Basilica.

Ruins of a 10th century church tucked away deep in a botanical garden.

A hospital where antique dolls are given new life.

At the crypt of St. Mary of Eulogies and the Dead you are left alone to ponder mortality among piles of skulls.

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

The only "Egyptian" pyramid in Europe and the legendary tomb of Remus.

The engineering wonder and pleasure dome of a much-maligned emperor still holds undiscovered secrets.

The remains of this ornate chapel now act as a portal to a cramped French cemetery.

A public park off the beaten path with a beautiful waterfall and 13th century Cistercian abbey.

Sacked by Vikings, blessed by William the Conqueror, dealt a fatal blow during the French Revolution—these ruins have seen it all.

The home of aviation trailblazers, in a remote corner of the big city.

Read between the lines of the subway map to find the hidden abandoned Civil War fort.

Lie in a hammock where George Washington stood.

This abandoned seaside fortress is now simply an imposing ruin being taken back by nature.

The remnants of two World's Fairs are here, complete with a 12-story globe, a mini-Manhattan, and a UFO-shaped pavilion.

Once America's longest-manned military fort, now an abandoned hulk.

The haunting, dilapidated remains of a former poorhouse on Staten Island's Greenbelt.

An abandoned Nazi explosives plant founded by the inventor of dynamite is now an underground museum.

This jaw-dropping 19th-century bridge uses its reflection to form what appears to be a perfect circle.

Once a giant gingerbread factory, this space now hosts exhibits and workshops on the historic treat.

This peculiar border irregularity is the only way to legally enter Russia without a visa.

Secret US military film studio in the Hollywood Hills.

The legendary building that needed ghostly approval before being built.

Palatial mansion estate used in films including "Flowers in the Attic" and "The Witches of Eastwick."