Despite its relatively small area, the island has much landscape diversity, which is explained by its complex geomorphology, in which there are stratovolcanic cones, calderas, lava flows, volcanic plateaus, various valleys, high and steep coastal ledges, sea terraces, and rocky beaches.

The terrain is undulating and steep with numerous hills, rising to two main peaks: The highest point is Mount Ketoy -(Russian: влк Кетой; Japanese 計吐夷岳; Ketoidake) with a height of 1,172 meters[2] to the east of the 1.5 km wide freshwater crater lake.

The second peak is Pallas -(Russian: влк Палласа; Japanese 白烟山; Shirokemuriyama) with a height of 993 meters in the center of the island, which is still an active volcano.

Ketoy had no permanent habitation prior to European contact, but was visited in summer by the Ainu tribes from Rasshua for hunting.

After World War II, the island came under the control of the Soviet Union, and is now administered as part of the Sakhalin Oblast of the Russian Federation.