The impressive Tower of Agios Petros lies 3 km northeast of Gavrio. It is a Classical-Hellenistic observatory dating from the 4th to the 3rd century B.C. The 20-meter tower is cylindrical and built of slate and has a diameter of 9.40 meters. It was used to protect locals from the raids of enemies and pirates. While parts of it have collapsed, the spiral stone staircase that led to the five floors still exists.
