This mansion oasis contains gardens, sculptures, and fountains just off the busy Plaça Kennedy in Sant Gervasi.

Occupied for six centuries by Franciscan Order nuns, this monastery is an amazing ode to Catalán Gothic architecture.

One of Antoni Gaudí's least-visited works, an homage to Catalan patrimony that mixes neo-Gothic with Modernista forms.

Bask in the 19th century grandeur of an eccentric Freemason millionaire's private gardens.

Mountain where Jesus was first tempted by the Devil.

Barcelona's historic 19th-century sewers, whose foundations were laid in medieval times, are open to the public for exploring.

These secluded and abandoned anti-aircraft defenses have become one the most scenic viewpoints in Barcelona.

A beautiful but toxic fountain of mercury.

This semi-secret storybook hedge maze is also the oldest garden in the city.

The last resting place of the famous Native American princess is marked by a haunting monument.

The longest hedge maze in the world.

A historic London pub with prison cells in the cellar and a "spy room" on the second floor.

Northern Ireland's Brobdingnagian stepping stones.

A strange rock with a sinister reputation lurks within the crimson waters of this Scottish glen.

Catacombs turned marketplace.

This 1920s Dutch barge is now a floating bookstore.

Famously misunderstood wonder of the ancient world

Winding paths and ramshackle mausoleums in the oldest "park cemetery" in London.

The popularity of Sherlock Holmes led to the creation of his fictional address, turning the orderly London street numbers askew.

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

The wooden grave marker of a railroad worker who died in a freak whirlwind.

This unique, full-sized copy of the Bayeux Tapestry sports a few modern additions, including underwear.

Soak up some local history in this restored Edwardian era swimming pool.

These caves secretly held national treasures during World War II.