Agia Marina is a hilltop hamlet 21km from Gytheio with only 15 permanent inhabitants. Due to its fortified position, it played a major role during the Ottoman Empire and later in the Greek Revolution in 1821. The sight not to be missed is the petrified forest that spreads along the sea. It is, actually, an outdoor geological museum with trunks of 2-3 million years-old that stand above the ground, a natural mosaic of fossil shells.