[3] Gastouni is situated in a flat rural area, 5 km from the Ionian Sea.

The river Pineios flows into the sea near Gastouni.

The Greek National Road 9/E55 (Patras - Pyrgos) and the railway from Patras to Pyrgos pass east of Gastouni.

There is a 12th-century Byzantine church in the southwestern quarter Katholiki.

[4] The municipal unit Gastouni is subdivided into the following communities: