Karimun Besar or Great Karimun, is mountainous at its N end, the principal peaks being Betina, 416m high standing 1.75 miles SW of the N extremity, and Djantan, 453m high, about 1.25 miles S of Betina.The S end of the island, except near Tanjung Balai, consists of low, swampy ground.
On the E side of Great Karimun, a bay is formed between Tanjung Bula Kasap, the NE point of the island, and Tanjung Sebatak, about 5 miles SSE. This bay is fouled by a shallow mud bank which extends about 1 mile offshore, out to the line of its entrance points.
Its main town, Tanjung Balai is a bustling port town with a lot of commerce, boosted by tourists from Singapore and Malaysia, however, it must not be confused with Tanjung Balai in North Sumatra province, a much larger city also known as Tanjung Balai Asahan and an international port. However, like Batam and Bintan, Karimun is also listed as a Free Trade Zone area.