Gastouni is a town and former municipality located in the Elis region of Greece. Following the 2011 local government reform, it became a municipal unit and the seat of the municipality of Pineios. The municipal unit covers an area of 59.325 km2.
The town is situated in a flat rural landscape approximately 5 km from the Ionian Sea, near the point where the river Pineios flows into the sea. It is positioned roughly 6 km south of Andravida and 11 km northwest of Amaliada. The Greek National Road 9/E55 and the railway connecting Patras to Pyrgos pass to the east of the town.
Notable local landmarks include a 12th-century Byzantine church located in the southwestern quarter known as Katholiki.