Heralded as the world's first theater, these ruins are often overlooked as they reside in the shadows of the Acropolis.

The railway carts travelers to central Athens's highest peak, which offers stunning vistas of the city.

This ancient Greek place of assembly and marketplace is being revealed layer by layer below the modern Athens cityscape.

An ancient octagonal weather station named for the eight Greek gods of wind.

This small 16th-century church in Athens is almost entirely surrounded by a modern building.

One of the few standing Roman lighthouses and a labyrinth of tunnels are a couple of the secrets at this historic castle.

A beautiful ruin of a 14th-century Plantagenet castle built by a medieval mercenary.

One of the oldest trees in Britain may have been witness to some of the country's formative moments.

The patch of land below the memorial was gifted by the British to the United States.

A six-ton wedding present for the King of the Scots.

A labyrinthine network of chambers with a storied past hides below Edinburgh's South Bridge.

This small museum in a 17th-century building honors three iconic Scottish writers.

The most loyal of little dogs, or a Victorian era publicity stunt?

Overlooked by many, the two famous Scottish warriors guard the main gate of Edinburgh Castle.

Protecting the dead from opportunistic body snatchers.

The final resting place of soldiers' loyal canine companions.

Berlin's beloved bear is immortalized at the Museum für Naturkunde.

Thousands of coffin-like pillars make up this controversial Holocaust memorial.

The largest free-standing aquarium in the world resides in a hotel lobby in Berlin.

Macabre astrological automaton clock dating to the late 1400s.

The hidden lair of an alchemist rediscovered in a 2002 flood.

A half-mile-long stretch of medieval forts built after a devastating pirate attack persists amid the modern port city.