This triumphal arch celebrating the Sun King's conquest of Lille is a masterpiece of military architecture.

This unusually-named reservoir found a second life as a nature preserve.

Catacombs turned marketplace.

London's largest outsider art museum.

This secluded walkway overlooks a magnificently wild London green space.

Wedged between two buildings at the Great Ormond Street Hospital is this secret music installation.

London's marvelous wildfowl reserve along the Thames.

A cluttered and astounding collection of antiquities and curiosities.

The world's first underground farm is in a World War II bomb shelter beneath the streets of London.

The "lost friend” is the most famous of the six moai statues that were removed from Easter Island.

These mysterious Viking chess pieces spent centuries hidden on a remote Scottish island.

Tucked inside a South Bank bar is an epic expressionist chronicle of the 20th century.

This ancient Egyptian obelisk still bears the wounds of World War I.

These ornate arches show how the course of the River Thames has changed.

The rose garden in Regent's Park where Pongo and Perdita met for the first time in Disney's "101 Dalmatians."

The Tudor-style cottage in the middle of the square is not quite what it seems.

A statue of the legendary Celtic warrior queen who fought the Roman invaders stands in one of the cities she once destroyed.

This macabre painting of a Shakespearean scene looks like something out of a nightmare.

A little slice of Japan and its aesthetics in London's Holland Park.

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

It is still illegal to "quarrel" at this unlikely urban oasis built on top of an electrical substation.

Never actually a tree at all, this spot was the site of London's public hangings for nearly 600 years.

A unique tribute to the millions of animals who served and died for the British military.

Following the trail of an old metro line, this scenic path is haunted by a creepy spriggan statue.