Mount Ossa, also named Kissavos, stands in eastern Thessaly, north-east of the city of Larissa. Its highest point is the peak of Profitis Ilias, at 1,978 metres. To the north, the Vale of Tempe separates it from Mount Olympus, and the Pineios River flows through that valley to the sea. Mount Pelion lies further south.

The western side faces the plain of Thessaly, and the eastern side drops to the Aegean Sea. The distance from the summit to the coast is short, so the mountain takes a lot of rain and snow from the sea, and fog is common near the top. The rock is limestone, and water has cut ravines, cliffs and caves into it. Above the forest the ground is bare, and on a clear day the view from the summit reaches Olympus, the plain and the sea.

The best-known walk is the climb to the summit. It starts at the mountain refuge at Kanalos, at 1,604 metres. The path is about three kilometres long and gains 500 metres, and it takes about an hour and a half. Red marks on the stones show the way. At the top is a small chapel of the Prophet Elijah, built under the ground. Walkers who want a longer day start in the village of Spilia. From there the national trail O2 climbs six kilometres through fir forest to the refuge. The O2 crosses the whole mountain on its way from Mount Olympus to Mount Pelion.

On the eastern side, a marked path leads through the forest to the Kalypso waterfall. From April to October, guides also take groups canyoning in the gorge, with rope descents down several waterfalls. An easier walk of about two and a half hours goes downhill from the village of Anatoli to the village of Metaxochori.

Forest covers a large part of the mountain. The Aesthetic Forest of Ossa has been protected since 1977 and covers about 165 square kilometres, and the mountain also belongs to the Natura 2000 network. Beech and fir grow on the higher slopes. Lower down there are chestnuts, oaks and maples, with plane trees along the streams and strawberry trees on the side of the sea. In autumn the beech forest changes colour.

On the eastern side, the Kalypso gorge runs down towards the coastal village of Kokkino Nero. In it is the Kalypso waterfall, about 70 metres high, with a pool at its foot where people swim in summer. The gorge has several more waterfalls. Wild boar, deer, foxes and jackals live in the forest.

The villages stand on the lower slopes, all around the mountain. Ambelakia, on the north-western side above the Vale of Tempe, became rich in the 18th century from red cotton thread, which its people dyed and sold through a cooperative. Stone mansions from those years still stand. The mansion of Georgios Schwarz, begun in 1787, is open to visitors. Its rooms have wall paintings and carved wood.

Spilia, at about 800 metres on the western side, is the village where walkers start for the summit. It has stone houses, a square under plane trees and a small church built against a rock. Anatoli, at about 960 metres on the southern side, looks towards the sea. Five kilometres from it, in the forest, is the 16th-century monastery of Timios Prodromos.