This Luxembourg cave is covered in cryptic looking marks left by mining activity.

One of the oldest scientific gardens in Britain, containing more than 13,302 plant species in its core collection.

17th century streets hidden under Edinburgh were once a breeding ground for the black death.

If you fly into Edinburgh Airport, it's possible to spot this prehistoric site without even getting off the plane.

Every birth, death, and marriage is recorded in these color-coded leather-bound books.

The tomb of one of Scotland's bloody historic villains is a magnet for bumbling desecrators.

This 16th-century house tells the city's history through old artifacts and quirky tales.

Protecting the dead from opportunistic body snatchers.

Come for the oysters, stay for the priceless art honoring inventors across history and Scotland's favorite outdoor sports.

A labyrinthine network of chambers with a storied past hides below Edinburgh's South Bridge.

A beautiful Greco-Roman structure houses a well once believed to have healing powers.

This grisly effigy displays an early Christian martyr who was skinned alive and beheaded.

Artistic tombs, monuments, and a beautiful "Hall of Fame" lurk inside this cemetery.

The odd depiction of the Virgin Mary and baby Jesus is rooted in the Catholic Church's eradication of Catharism.

Small on the outside, big on the inside, this church is an astonishing act of visual deception.

Milan's duomo is covered in beautiful carving including a curious "dinosaur-like" beast.

Long-abandoned art nouveau baths beneath Milan's Piazza Oberdan.

The secret medieval communication system will whisk your words above the noise of the crowd.

A Milanese café entirely designed by the American director Wes Anderson.

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

A treasure trove of Renaissance-era funerary art in a Roman church built on top of Nero's grave.

This former Roman Catholic Church still contains the embalmed hearts and organs of 22 popes.

Roman politician Herodes Atticus built this nymphaeum to honor his wife, whom he may have murdered.

This small, ancient Roman temple was once a church dedicated to the patron saint of penitents.