The intricate stonework of Machu Picchu serves as a testament to Incan engineers.

An Italian hillside ghost town.

An ossuary built in 1210 to collect bones from the Ospedale Maggiore of Milan.

The doodles of a genius line the walls of a secret room under the Medici Chapel, where they were hidden for nearly 500 years.

The longest living non-clonal organisms on Earth.

2300-year-old Roman road connecting the empire.

The hallucinogenic center of the ancient world.

Geothermal waterfalls in Tuscany.

Each spring, a dreamlike carpet of bluebells overtakes the forest floor.

A small museum filled with over 1,000 clocks, and one particular clock calibrated to run until the year 9999.

Stalactites and stalagmites in a beautifully lit cave.

Thousands of well-dressed mummies below a monastery.

If drivers cross the rumble strip on this stretch of Route 66 at just the right speed it plays "America the Beautiful."

A breathtaking array of ancient Pueblo structures and artifacts counterintuitively preserved by neglect.

An alchemist's "magic door" stands in the middle of a Roman park.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

The first declared National Monument in the United States.

The deepest lake in the United States, and once the site of epic destruction that lives on in legends.

Famously misunderstood wonder of the ancient world

This 1,300 year old monastery built atop a single rock was once only accessible depending on the whims of the tide.

19th century pendulum and a clock restored by a rogue group of guerilla artists.

A horde of stray cats rule in this secluded Parisian cemetery under a bridge.

The only substantial part of Nazi Germany's formidable defensive line through Northern Italy that survives today, largely intact.

Memorials at a Florence railway station remember the citizens who were deported from Italy and sent to extermination camps.