A hidden three-foot-wide house separates these two regal churches.

A headstone notes where the most famous of Robin Hood's legendary Merry Men is reportedly buried.

An exhibition of preserved locomotives housed in a 1950s depot shows the history of Denmark's railway.

A unique, modernist church tower that appears to float above the ground.

Whisper secrets in a busy station only to be heard on the other side of this acoustic arch.

This 19th-century island fort built to protect against an invasion by sea.

This remote island, home to the easternmost point in Denmark, once hosted pirates and a military fortress.

An abandoned bear enclosure from a 19th-century zoo located in a Danish forest.

This elaborate High Victorian Gothic structure is one of the world's few 16-sided buildings.

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

150 or so scrounged-up lamps, chandeliers, and lanterns light up this alley in central Athens.

These caves secretly held national treasures during World War II.

This small museum once served as a royal hunting pavilion for King Otto Friedrich Ludwig.

A Byzantine church containing the holy remnants of three saints sits atop the site of an ancient temple.

There are many Byzantine-era churches still standing in Athens, but this is the only one with a 2,500-year-old column rising through its roof.

This small 16th-century church in Athens is almost entirely surrounded by a modern building.

This ancient hydrological marvel is now the base of a modern outdoor cinema.

Heralded as the world's first theater, these ruins are often overlooked as they reside in the shadows of the Acropolis.

A 2,000-year-old computer demonstrates remarkable engineering and astronomical precision.

Legend says this sacred tree was a gift from goddess Athena.

The ruined doorway is a portal to the building's turbulent and torturous past.

An ancient octagonal weather station named for the eight Greek gods of wind.

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

A man's head is enshrined beneath a statue near the first building constructed for the modern Olympic Games.