World's first "penitentiary," meant to be humane, drove men insane.

A collision of human error and natural geothermal pressure created this rainbow-colored geologic wonder.

Rippling sand dunes frozen in the Arizona rock.

This iconic L.A. bookshop is housed in an abandoned bank—both symbolic and chic.

La Monte Young and Marian Zazeela's "Dream House" will immerse you in an ever changing world of sound and light.

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

An artsy hidden staircase leads to breathtaking views of San Francisco.

A psychedelic labyrinth on the San Francisco bay.

A terrific purveyor of natural history objects and curios.

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

A relic of Victorian grandeur hides beneath a busy South London road.

The Columbia Road Flower Market is now open every Sunday, rain or shine.

This beautiful Victorian ironwork masterpiece was built to keep London from smelling like poop.

A network of concealed passageways lies within a busy London Underground station.

An artistic tribute to the famous singer, just around the corner from where he was born.

This massive collection of British military artifacts includes the heartbreaking personal letters of the men in the trenches of WWI.

Thanks to modern navigational tools we now know that the true prime meridian runs through a park next door.

The Metropolitan Police refurbished the blue box (perhaps not coincidentally) the same year "Doctor Who" returned to TV screens.

London's old-school healing garden.

This hidden green space is the city's second largest conservatory.

London's smallest police station is barely the size of a phone booth.

The remains of Crystal Palace Great Exhibition of 1851.

This 1920s Dutch barge is now a floating bookstore.

Remnants of a Victorian garden feature sitting in public woodland.