The highest peak of the range of mountains in the northern Peloponnese described by this name is Psili Korfi (literally, High Summit), at 2355 meters( 7724 feet).
This little visited area is one of the best in all of Greece for the naturalist, with many habitats and diverse wildlife of all kinds.
The region is generally damper than the mountains in the south Peloponnese, and there are large forested areas, particularly in the eastern part.
Flora is very rich and diverse here, with species adapted to areas that aren't heavily grazed.
The best areas in this region is very difficult to access, this the upper valley of the River Styx, with the dirt road south from Peristera probably the best way in, followed by an ascending path (which is waymarked), and which gets very rough at the high end.
From about 1800 meters and up, where the trees thin out, beautiful plants are found on the steep limestone cliffs and rocks, some of them endemic. Two plants related to the borages is found on scree slopes and crevices, both found nowhere else in Europe except on Mt. Giona, and one of them with lovely yellow blossoms; a beautiful sage is also found here, among other plants.
The cave from which issues the mythical River Styx is found at about 1900 meters, with a waterfall flowing over it during part of the year, which area constitutes perfect habitat for some flowers that bloom into the summer, including a saxifrage and a columbine that grows inside the cave.
Birds include alpine choughs, crag martins, ravens, common kestrels, and others; there is a wide range of butterflies in this range as well, some of them quite rare.
The high parts of the Helmos range can be reached from the road that goes to the Kalavryta ski center, and on to the EOS refuge, which is at over 2000 meters. There are paths from here across the summit ridges and down into the Styx valley, but only for the hardy.
A huge forested area surrounds the slopes of Helmos, with Greek fir, oaks (including Hungarian) and pines.
A dirt road from Zarouckhla to Feneos passes through a mixed forest with many orchids and other flowers.
Butterflies are found in the clearings, birds in the forest, especially in spring, and there are beech martens also in the woods.