Bring your own cardboard to the slippery slopes of concrete hidden in a neighborhood park.

World's largest collection of serial killer artwork and other macabre exhibits.

An exquisite tunnel of cascading flowers.

A peculiar mansion built by the troubled heir to the Winchester Rifle Company fortune.

A beautiful and abandoned New York subway station from 1904, complete with chandelier.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

A collection of more than 12,000 shoes, displayed in a building shaped like a shoebox.

This Toronto garden collects stares and tchotchkes in equal measure.

One of Canada's most incredible rare book collections holds hundreds of thousands of gorgeous tomes that the general public can touch.

Try not to get slimed in Tribeca.

A partially hidden wall graffitied by spectators of the 1976 Bicentennial, recently rediscovered.

A single handprint, which, according to Ohio State University legend, cannot be scrubbed off.

Louise Bourgeois' 30-foot-tall steel spider sculpture.

The Victorian-era greenhouse is stuffed with tropical plants, and open 365 days a year.

A 98-room castle in the middle of Toronto that bankrupted a 19th century electricity multimillionaire.

A one-of-a-kind collection of a unique medium.

The L.A. Zoo has a secret garden of rare bootleg cycads, a palm specimen dating back 280 million years.

Hidden in the hills of Hollywood, this secluded Oz-themed garden is dotted with dozens of thrones.

This opulent hotel has been visited by Spider-Man, Charlie's Angels, and the Ghostbusters.

This brightly made over hotel hides decades of suicide, serial killers, and mysterious deaths.

An eccentric home stands out in an otherwise average neighborhood with mosaics, mini topiaries, and kinetic sculpture.

A psychedelic labyrinth on the San Francisco bay.

A historic house in St. Louis was plagued by a series of suicides committed by family members involved in a successful brewery.

An acoustic anomaly with a mysterious cause.