An ancient Egyptian temple in the middle of Madrid, Spain.

Madrid's romantically ornate crystal palace has been offering shelter to plants and art for over a century.

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

The Vatican's secret porn-festooned bathroom was painted in erotic murals by one of the greatest artists of the Renaissance.

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

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

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

This demon atop the Notre-Dame de Paris looks utterly bored.

Stripes of human ashes cover a back lawn in the most sought-after burial grounds in Paris.

A 400-year-old church covered floor to ceiling in ex-voto offerings from the faithful.

The industrial architecture honors the laborers who brought the Exposition Universelle of 1900 to life.

A 16th-century fountain marks the site of a lost medieval cemetery once filled with mass graves.

A popular shrine where the Blessed Virgin allegedly appeared in 1830, displaying a holy armchair and two incorruptible remains of Lady Saints.

This life-size replica of the Statue of Liberty's flame is also a tribute to Princess Diana by default.

A majestic lion statue guards this Parisian botanical garden, and feeds on an unsettling item.

Exquisite wall sculptures carved in secret by an early quarryman in an obscure corner of the Paris Catacombs.

19th century pendulum and a clock restored by a rogue group of guerilla artists.

This statue was given to France by the United States to commemorate the centennial of the French Revolution.

This iconic Parisian bookstore doubles as the "Tumbleweed Hotel" for traveling writers.

France's most famous cemetery, with some of its most curious tombs.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

A huge, bustling local market in Panama City.

Believe it or not, the now-ubiquitous California avocado originated in Guatemala.

This restored colonial house was once home to the botanist responsible for bringing avocados to the U.S.