Dr Barnes' $25 billion private collection of art and arboretum.

The oldest surviving botanic garden in the United States.

Tour the dark and beloved poet's former cobwebbed basement, which may have inspired "The Black Cat."

Philadelphia boasts one of the best — and most often overlooked — traditional Japanese gardens in North America.

An abandoned cemetery lies in ruins as the surrounding forest swallows it whole.

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

America's most famous museum of medical oddities is home to the remains of Albert Einstein's brain.

Locals purchased this abandoned quarry in order to make sure it continues to be overgrown.

An small and easily overlooked archaeology museum chock full of Egyptian artifacts.

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

Scattered throughout London are ancient remnants of the city's former bounding wall.

The only university zoological museum in London houses extinct animals, bizarre natural history specimens, and a Micrarium of microscopic creatures.

This small collection of rare books was uniquely locked up for safe keeping.

Rebuilt remains of a temple to Roman god Mithras.

London's old-school healing garden.

A memorial to a dog that inspired rioting in the streets of London.

Giant, friendly pelicans in Central London, the most unlikely of places.

The perfectly preserved underground rooms where Churchill plotted the war against Germany.

A closed London rail station created to cart away the dead still bears the marks of attempts to make it less morbid.

The breadfruit-adorned final resting place of the infamous Captain of the HMS Bounty.

The "beautiful" equation predicting the movement of all electromagnetic particles is engraved in front of Newton's tomb.

A tribute to the couples who brave long periods of separation during wartime.

A memorial sculpture to heath hens stands on the spot where the last heath hen, Booming Ben, was last seen.

Stay at this storybook estate, featuring Sir Henry Hudson Kitson's masterpiece "Gingerbread House."