Megalopoli is situated in a wide valley, surrounded by mountains: the Taygetus to the south, the Mainalo to the north, the Tsemperou to the southeast and the Lykaion to the west. Its elevation is 430 m above sea level. The river Alfeios flows through this valley, coming from the east and flowing to the north, passing south and west of the town. Its tributary Elissonas passes north of the town. The large lignite deposits around Megalopoli are being exploited by open-pit mining. The Megalopoli Power Plant, 3 km northwest of the town centre, has produced electricity from this lignite since 1969.