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

This architecturally eclectic fortress witnessed centuries of bloody turmoil, including the massacre of its ruling clan.

Monumental sculptures guard many of the graves, transforming this necropolis into an open-air fine art museum.

A fortress built to pacify local uprising that had a stint as a Nazi concentration camp before becoming a five-star hotel.

A sharp sculpture made of thousands of pieces of jagged glass.

Little Red Lighthouse under the George Washington Bridge.

Visit the monolithic tomb of America's most famous general.

This sculpture by artist Fritz Keonig survived the 9/11 attacks and now stands as a monument to the victims.

The "Seinfeld" diner.

Elevated freight railway turned wildly successful urban park.

This 1000 year old relic-filled cave monastery and UNESCO World Heritage Site also hosts an amazing micro-miniature museum.

Tower with a double-helix spiral, adorned with letters of the Georgian alphabet.

A literally moving statue of stacked metal giants just continually trying (and failing) to find love.

The first skyscraper to include a Ferris wheel built into the facade.

When flour explodes, it's not a pretty sight.

A toweringly silly piece of modern art has been delighting locals since the 1980s.

The only arched bridge made of stone on the entire Mississippi River.

This old residential building was once the largest flour mill in the world.

The birthplace of Karl Marx is now a museum dedicated to the communist revolutionary's life and work.

The last bastion of Roman presence north of the Alps looms over a German town.

An expansive complex of subterranean tunnels is all that remains of one of Europe's most formidable medieval fortresses.

Rotterdammers' dirty minds gave this santa a dirty nickname and cursed it to a life of wandering.

These slanted cubic abodes are a creative if odd solution to a zoning pickle.

Terrifying derelict military hospital once housed a recuperating Hitler.