The popularity of Sherlock Holmes led to the creation of his fictional address, turning the orderly London street numbers askew.

Once the tallest building in the world, this abandoned church is now a monument to the destruction of WWII.

Böttcherstraße's bells, extolling Nordic virtues and the great conquerors of the world.

A stunning gilt bronze relief denounced by Hitler as "degenerate art"—even though it was dedicated to the Nazi leader.

The glowing blue Nymphaeum of Emperor Tiberius.

Suffocating dogs was a common spectacle in the fumes of this noxious cave.

A sulfuric hellscape in southern Italy.

Italy's third-largest Roman arena gives a peek into the underground operations beneath the ancient spectacles.

Italy's "New Mountain" rose from the ground in a volcanic eruption in 1538.

Smack-dab in Campania’s volcanic fields, this scenic lake was once thought to be the gate of hell.

Virgil's many-mouthed gateway to the underworld.

Two geological phenomena in one precarious locale: a towering stone window, and a deep blue void.

The fishing boats that moor in this small lagoon enter and leave through a tunnel to the sea.

This 19th-century aqueduct provides insights into how water was supplied to Victoria on the island of Gozo before modern plumbing.

People have been making salt here using traditional methods for centuries.

This unique building in the main square stands out among the city's typically Baroque architecture.

A World War II-era sign in Valletta is a reminder of when Malta was besieged so severely that food needed to be rationed.

The floor of this spectacular Baroque sanctuary is covered in memento mori.

A haven for book enthusiasts across the street from Retiro Park.

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

Along the pavement of this neighborhood in Madrid are quotes from famous authors.

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

A rare set of strings by famed instrument maker Antonio Stradivarius is on display in the Royal Palace.

A stone slab in Madrid marks the point from which the distances of Spain's national roads are measured.