Oku is a very mountainous region, around 1,200 metres (3,900 ft) above sea level, and thus rather cool considering its latitude. It is not cold enough for snow, but at night during the dry season temperatures drop below human comfort range. Mount Oku, a stratovolcano, reaches a height of 3011 metres (9880 feet) and is the second highest mountain of Cameroon after Mount Fako (better known as Mount Cameroon).
The broader Oku or Foumbot volcanic field also includes many scoria cones and maars, several of which are filled by crater lakes. Lake Oku is a crater lake. Two of the crater lakes, Lake Nyos and Lake Monoun, have been the subject of extensive research. Quantities of gas build up in the lakes and are occasionally released; being heavier than air, they pour down the mountainside and can suffocate entire villages. Some of the locals believe that a god lives in the lake and must be appeased.
The region is an important one for biodiversity, especially the Kelum mountain Forest.