The world's longest known cave system.

This modern castle sat empty for decades before a fire inspired its builders to complete its luxury halls.

A full-scale replica of a 1774 colonial settlement in Kentucky.

Eight rare Corvettes are swallowed up by a sinkhole in Kentucky's National Corvette Museum.

Amazing taxidermy dioramas from the 1960s in a cement building meant to look like an ice cave.

This grave marks the final resting place of a legendary frontiersman... unless it doesn't.

This huge clock made of flowers and simple machinery was once used a political weapon.

After a water tower painting was accused of being an ad, a simple fix was made that gave the city a motto.

World's largest collection of Coke-related items not held by the Coca-Cola company.

The oldest operating Mississippi River–style steamboat still navigates the Ohio River.

The medieval "Bearded Man" relief still serves as a clever flood warning marker.

A plaque marks the spot where the saint was shoved off the Charles Bridge and into the river.

Microscopic scenes; some call it novelty, some call it art.

Two stunning 17th-century libraries and a cabinet of curiosities.

Around 100,000 bodies are buried below the medieval headstones, many of which mark graves with multiple bodies stacked up to 12 deep.

Synagogue built from the stones of Solomon's temple contains the golem of Prague.

Breathtaking and huge 430 year old maps of Italy.

Romans decided this 16th-century "talking statue" was so ugly, they named it after a primate.

Hidden beneath the famous St. Peter's Basilica is a veritable city of the dead that may hold the remains of St. Peter himself.

Historic fortifications form the boundary of Vatican City, but it’s not entirely surrounded by walls.

This equestrian statue of Constantine the Great has been the subject of criticism for centuries.

One of the few remaining ancient aqueducts described by Frontinus as 'the most solemn testimony of the Empire.'

A must for film lovers in Madrid and home to the Spanish Film Library's projection space.

Ruins battered by centuries of war and disaster offer a wondrous glimpse of medieval Ireland.