Hiding the longest subterranean river known in the world.

Descend into the tunnels to experience the life of a coal miner.

This giant urban staircase was built to keep the city's brave fighting men from getting waylaid in the red light district.

A once-magnificent collegiate church is falling into ruin.

This abandoned Belgian fortress is purposefully being left to nature.

Museum covers every step of the chocolate-making process, from cultivation to the finished product.

A marble Lucifer hides behind the pulpit of this Gothic cathedral.

This oddly shaped church resembles a rocket.

A king's pet, a pope's gift, an artist's inspiration, and a tragic shipwreck.

Elaborately carved to showcase the glorious wealth that the age of exploration brought to the Portuguese empire.

This Industrial Age architectural and engineering gem helps visitors and residents alike traverse Lisbon, “The City of Seven Hills.”

These ruins in Volvi were once at the intersection of the Eastern and Western Worlds.

Thousands of rusting train cars have been slowly falling apart on the edge of Greece's second largest city.

A two thousand year old brothel uncovered in Northern Greece.

This architecturally eclectic early-20th century mosque was built as a place of worship for the Islamic followers of a Jewish messiah.

This field of half-buried stone crosses was the burial place of a sect of heretical gnostics.

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

The ghost town where the villagers refuse to leave.

This open air archeological site houses almost as much wildlife as it does classical religious artifacts.

Monasteries on rock pillars, once accessible only by frayed ropes.

Explore 400,000 years of humans' "battle against darkness" in this offbeat but thorough lamp museum.

Ordinary art transforms to extraordinary thanks to locals' quirky sense of humor.

A vintage video game wonderland in downtown Reykjavik.

Puffin enthusiasts flock to Europe's largest seabird cliff, which over one million birds call home.