In the northeastern part of Achaea you can find the mount Helmos.

Helmos (less known by the ancient name Aroania Mountains) is the third highest mountain in the Peloponnese, after Taygetos and Kyllini. The highest point of Helmos is Psili Koryfi (High Peak) in 2335 m. Other peaks of Helmos is Neraidorahi (2,340 meters), the Prophet Elias (2,238 meters), Gardiki (2,182 meters), Avgo (Egg) (2138 meters) and Nisi (2,042 meters).

In Helmos at 800 meters altitude lies the Tsivlou lake, created after a natural landslide in the riverbed Karthi (800 m.), while near the mountain's peaks the seasonal lake Mavrolimni is formed from melting snow.

Myth has is that Styga, one of the rivers that flew into Hades, stemmed from Helmos mountain. The ancient took oath in its sacred waters and its violation ensued terrible punishment. According to Homer, Thetis plunged the mythical hero Achilles into Styga in order to make him immortal, leaving only the point of the heel from which she held him vulnerable (where he was eventually injured by arrow and killed).

Helmos is ideal for hiking and climbing, being at certain points so rough that it constitutes a challenge even for the most experienced climbers.