This ancient Greek place of assembly and marketplace is being revealed layer by layer below the modern Athens cityscape.

This fortress dates back to the 6th century and is also the site of a controversial abandoned restoration project.

A tiny church on a man-made island in the Adriatic.

These historic defenses ensured the city within would survive hundreds of years of occupations, sieges, and invasions.

Backwards hour and minute hands and a timing mechanism that fluctuates with the temperature led to this clock tower's local nickname.

A towering spire in the fortress of Kalemegdan honors the victorious armies of Serbia during their struggles against the Ottoman Empire.

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

Nikola Tesla's ashes are held in a golden sphere, surrounded by his works.

A tribute to an iconic act of defiance from the Croatian War of Independence involving a small car.

A number of craters left by fatal mortar strikes have been filled with red resin to remember those lost during the Siege of Sarajevo.

Oriental bazaar in the heart of Sarajevo.

The place where World War I began.

Bridge that died in war and was resurected.

According to a local legend, this old castle could only be built after a woman was immured in the walls.

Once the fallout shelter of a dictator, this sprawling bunker is now a combined history museum and contemporary art gallery.

The elliptical citadel resisted the advance of the mighty Ottomans several times, thanks to the military prowess of the "Dragon of Albania."

This demon atop the Notre-Dame de Paris looks utterly bored.

An immersive projection art installation uses sound, scale, and light to take visitors inside classic works of art.

Eighty million natural history specimens call this gargantuan museum home.

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

The deepest underground city in Turkey was designed to protect 20,000 people behind massive stone doors.

With over 10,000 lights, this engineering marvel lights up the city after dark.

Also known as the "Red Taj Mahal."

An imperial fortress city that incorporated cultural elements from the entire Mughal empire, only to be abandoned the year it was finished.