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

Six ravens are kept captive (but well-fed) at the Tower of London to prevent the fall of the Crown.

Northern Ireland's Brobdingnagian stepping stones.

The atmospheric road was never meant to be so creepy.

A 1,215-foot tunnel transports pedestrians beneath the River Thames.

The bears of Bern have been a city highlight for over 500 years.

A cablecar-station-turned-revolving restaurant with 360-degree views of the Swiss skyline.

This historic covered bridge contains a series of macabre paintings that communicate one thing: everyone dies.

A historic observatory precariously perched at the "Top of Europe."

This memorial commemorating fallen Swiss Guards of the French Revolution has been called the saddest stone in the world.

Destroyed Serbian army headquarters sits half crumbled in a largely revitalized Belgrade.

This 14th century castle withstood years of battle but is now sliding off the hills into the Danube.

This communist behemoth is the heaviest building in the world and a legacy of a brutal regime.

A giant portrait of an ancient king looms over the river.

This castle has links to Portugal’s founding and struggles for independence.

Eat the ultimate iteration of Portugal's most beloved pastry.

Elaborate tile work in this railway station tells the story of Portugal.

Portugal's National Pantheon has a history of curses, collapses and financial problems.

An ancient and majestic fortress that played an integral role in Portugal's road to independence.

Elaborately carved to showcase the glorious wealth that the age of exploration brought to the Portuguese empire.

A king's pet, a pope's gift, an artist's inspiration, and a tragic shipwreck.

This Industrial Age architectural and engineering gem helps visitors and residents alike traverse Lisbon, “The City of Seven Hills.”

This unreal Portuguese palace looks as though it's made from a pile of different castles.

One of the most beautiful bookstores in the world hides a neo-Gothic interior behind an art nouveau facade.