Plaques on its facade commemorate the Tiber's most destructive deluges.

Remnants of a 4th-century church with vivid medieval frescoes and ancient sarcophagi hide beneath this old basilica.

A fortified medieval basilica on the Caelian Hill preserves extraordinary frescoes and one of Rome's most beautiful hidden cloisters.

An atmospheric, medieval-themed book store hides in a 13th-century underground space.

This emotive sculpture was originally created for the 1878 World's Fair.

The commemorative stone column conceals a secret laboratory.

This medieval manuscript collection has some of the most obscure and ancient texts in the world.

Thousands of biblical and pagan images are carved into this small 12th-century church.

300-year-old villagers houses and traditional churches preserve a nearly lost piece of Russian history.

Specimens collected by the author of "Lolita" and self-taught lepidopterist are exhibited in his childhood home.

An ever-growing literary collection housed in the apartment where the Russian author penned his final novel.

A 250-year-old timepiece-automaton adorned with golden mechanical birds, which still sing to this day.

Some Moscow residents once claimed the bizarre, contorted mass of metal on top of the building was used to manipulate minds.

Every day is like Christmas on this street where the traditional Neapolitan nativity scene comes to life.

The approximate spot where the last Grand Master of the Knights Templar was put to death.

The narrowest street in Paris.

An incredible mosaic-lined monument said to have held the remains of an ancient Roman empress.

This facility has manufactured stunning tapestries for France's royalty ever since the 17th century.

Spanish architects used seized Muslim gravestones to rebuild parts of the fortress.

The cathedral stands in New Jufa, Isfahan's Armenian quarter that was established in 1606.

A medieval, mosaic-lined baptistry built by a heretical Christian sect.

A mysterious shape catches the eye in this 16th-century painting.

Psychoanalyst Carl Jung reported a paranormal experience after visiting this mosaic-lined Roman baptistry.

The first modernist church in Europe.