An unusual round church in London with a Templar past.

Scattered throughout London are ancient remnants of the city's former bounding wall.

Rebuilt remains of a temple to Roman god Mithras.

This bridge was constructed from the rubble of the infamous Bastille.

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

A large grotto built in the 16th century amidst Florence's famous Boboli gardens.

Renaissance hospital featuring a rotating door into which unwanted babies were dropped.

Picturesque intersection of witchcraft and ancient Christianity.

This eccentrically decorated palace is replete with grottoes, fountains, tunnels, and caves.

Houses are tucked between, on, and underneath giant boulders.

A king's pet, a pope's gift, an artist's inspiration, and a tragic shipwreck.

Legacy of the earthquake that nearly wiped Lisbon off the face of the Earth.

Ancient catacombs form the foundation for this Rococo orgy of a church.

An Irish church where an 800-year-old mummy is reaching out of his coffin as if to shake hands.

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

A 16th century chapel decorated with bones, skulls, and entire bodies hanging from the wall.

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

One of the largest Roman settlements in Portugal.

The corpse bride of Portugal.