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

The underground sanctuary of a mysterious ancient cult.

The yawning maw of this pagan visage is said to bite off the hands of liars.

The "Great Sewer" of ancient Rome is one of the oldest sewer systems in the world, and is still in use.

This is the oldest Roman-made bridge in the city still existing in its original state.

Inside the cloister of the Temple of San Juan Bautista is a ceiling decorated with gold Baroque illustrations.

In Coyoacán, a pair of coyotes crown a public fountain in reference to the ancient Aztec name of the borough.

Frida Kahlo's childhood home, now a museum of her life and works.

The grand, column-fronted, sculpture-adorned home of the ambitious digital library.

One of few lasting examples of the brief octagon craze that developed into folly.

27-room home built with the fortune of a sugar magnate.

San Francisco's oldest operating hotel, with a Victorian atmosphere and a "haunted" fourth floor.

The tea room that pushed the boundaries of adorable straight into... we can't find the words.

This turn of the century masterpiece has a mysterious goaty interloper.

The best place in the park to test out your throwing arm.

San Francisco’s century-old Christmas Tree.

This shop specializes in oddities and Victorian-inspired wonders.

This private residence was the template for one of the most beloved television homes of all time.

The house where the writer spent his formative years.

The gorgeous library at Trinity College is home to remarkable treasures of Irish identity.

The somber sculptures commemorating Irish Famine on the river Liffey in Dublin.

Dublin's most modern, visually spectacular bridge is modeled after Ireland's national emblem.

A preserved oasis with traditional Andalusian-style architecture and beautiful views of the Nile.

The exorbitant price of paradise.