A sinkhole and now a swimming hole, too, full of dazzling turquoise water.

Standing atop 2nd-century Roman ruins, this church is one of the oldest and most iconic in Old Cairo.

This ancient structure is widely thought to be the oldest intact pyramid in the world.

Climb to the top of its spiral spire for spectacular views of Copenhagen.

A natural wonder in south Denmark.

The de facto symbol of Copenhagen is this bronze fairytale which cannot seem to keep its head for very long.

In one of the world's smallest countries, a royal's personal winery is open to the public.

This exclusive resort has completely covered a tiny Balkan island in a 5-star warren of guest rooms.

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

A curious cave church carved into the face of a cliff.

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

Along the Palisades skyline are the ruins of a large mansion built in 1911 and demolished in the 1930s.

A riverfront park that both remediated and preserved its industrial past.

A former connection to City Island, it has been abandoned since the 1930s.

Outdoor escalators and art have helped change what was once a notoriously dangerous part of Medellín.

Home to 23 voluptuous and instantly lovable sculptures by one of Latin America's most celebrated artists.

Ripped apart by a bomb in 1993, the shell of Pablo Escobar's infamous vacation house still stands.

An unusual and beautiful form of mass transit serves the city's steepest neighborhoods.

A 10 million-ton rock once worshiped by the Tahamies Indians, accessed by an astounding staircase.

The largest Roman amphitheater in the Balkans once held over 20,000 people, but managed to lay hidden for hundreds of years.

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

What happens when you cross a mayor and a painter?

This ominous Albanian fortress houses tanks and downed planes as a reminder of their victories over Western imperialism.

Hundreds of thousands of concrete bunkers crowd Albania long after the fall of Communism.