The Girmeler Cave, located nearly 30 km far from Fethiye in the territory of the famous ancient Lycian city of Tlos, is one of the earliest settlements of western Turkey. This karstic cave is composed of two long galleries, each with impressive entrances. The cave A located at the eastern side has a 16 m wide opening with a 40 m long gallery. A small gallery is also attached to the main gallery at the back. The cave B located at the western side has an impressive gallery of 150 m long with an opening measuring 15 m in width. Because no archaeological investigation have so far been carried inside the caves A and B, it is not clear whether or not the interiors were occupied during prehistoric times. However, recent archaeological studies conducted in front of the cave by a small team from the Tlos Excavations show that the front of the caves was first occupied as a settlement as early as the end of the ninth millennium BC in the Mesolithic period. Thus, the Girmeler Cave is among the rare examples with evidence for a Mesolithic habitation in western Turkey. The first inhabitants occupying the front of the cave were probably hunter gatherers. The site was evidently continued to be settled during the Neolithic and Chalcolithic periods. The remains representing the Neolithic and Chalcolithic periods have been attested on top of the Mesolithic levels of occupation. Around 6000 BC, the cave began to be settled by agriculturalists exploiting the resources around the cave. The remains of Neolithic and Chalcolithic settlements formed a 7 m high and 55 m wide mound in front of the entrances of the cave. The front of the cave was evidently used as thermal springs from the classical antiquity to the present, resulting in the destruction of the prehistoric mound to a great extent. The prehistoric mound was also destroyed by illicit digs. The topmost layers of the mound yielded evidence for the Iron Age, Roman, Byzantine, and Ottoman occupations.