This historic address is home to the beloved ball and is an almost totally empty building among the most expensive real estate in the world.

This abandoned subway station beneath the Waldorf-Astoria hotel is allegedly used to secretly transport presidents.

Macabre symbols of death and mummies on display set the tone of this Italian purgatory church.

A cavernous three-story, 43,800-square-foot basement that was forgotten about for 60 years.

Plundered and left asunder by grave robbers, this ancient necropolis has been painstakingly pieced back together.

Dogs, cats, horses, monkeys, frogs, and fish are laid to rest at the second-oldest pet cemetery in the U.S.

A home built with marble tombstones from the graves of 2,200 Union soldiers buried in a Virginia cemetery.

This hidden stream beneath Indianapolis makes an appearance in the best-selling novel "Underground Airlines."

The de facto symbol of Copenhagen is this bronze fairytale which cannot seem to keep its head for very long.

This giant crucifix is like U2's Joshua Tree for Swedish death metal fans.

This endearingly discomfited urinating statue commemorates the sneaky pees had by us all.

A subterranean house of worship carved right out of the bedrock.

Superstitious? Discover the witchy side of Mexico through its largest esoteric market.

This church devoted to Mexico's "dead saint" is a festive celebration of a formerly hidden religious figure.

This landmark church concealed a crypt packed with bones that was discovered thanks to the London Blitz.

The mass grave of a heroic Revolutionary War regiment sits below an empty lot near the Gowanus Canal.

A neo-Gothic temple in central Mexico featuring a labyrinthine network of crypts.

An Industrial Revolution-era public work that purified water using nothing but sand.

A steam powered train that runs on city streets.

An eerie, derelict amusement park in Berlin.

Berlin's oldest surviving academic architecture hosted decades of animal dissections.

Home to 10,000 medical specimens including the remains of Rudolf Virchow's extensive collection of pathological specimens.

Swedish mice can dine at the Nuts of Life restaurant or take a date to the amousement park.

From Coke II to Google Glass, this exhibit features some of the most spectacular commercial flops.