Traditional 11th-century outdoor tannery.

Thousands of narrow alleyways in an ancient medieval city make up what's believed to be the world's largest car-free urban zone.

The other side is actually green.

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

The oldest restaurant in the world is this old-world Spanish eatery, still known for its suckling pig.

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

One of Madrid's oldest trees, with a long and colorful history, resides in El Retiro Park.

A lush indoor jungle fills this bustling Madrid transportation hub.

The only urban monument in the world designed by the great surrealist painter Salvador Dalí.

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

Its columns were all carved from the same white oak tree.

The biggest museum dedicated to insects in North America, one of the largest in the world.

This 1967 experiment in modular architecture was designed to be a new model for urban living.

The lost Latin words were reconstructed using the holes from the nails that once pinned them in place.

A natural arch carved by a river gave its name to the so-called "Cave of Forgotten Dreams."

These quaint French houses dangle precariously over a precipice.

One of the longest wooden benches in the world snakes around Geneva's Treille Promenade.

Large Hadron Collider and the Birthplace of World Wide Web.

What once sat in the world’s spotlight is today a largely disused ghost complex.

This building displays the scars of the “Dekemvriana,” a dark time in modern Greek history.

The only ancient site that remains on the south bank of the sacred Ilissos river.

According to legend, this ancient column contains healing properties.

Underneath one of the region's most historic roads lies the home of Plato's successor.

A tiny Greek Orthodox church from the Ottoman era hides on a busy city street.