Complex sentence: It is almost entirely formed of mountains, including the Tymfristos and the Panaitoliko in the south, rivers including the Acheloos in the west, Agrafiotis to the east, and Megdova in the east flowing down to the Ionian Sea.
Split into simpler sentences: It is almost entirely formed of mountains, including the Tymfristos and the Panaitoliko in the south. It's rivers include the Acheloos in the west, Agrafiotis to the east, and Megdova in the east flowing down to the Ionian Sea.