Armutlu Peninsula is between Gulf of Izmit in the north and Gulf of Gemlik in the south. The westernmost point of the peninsula is the cape of Bozburun. The bird's flight distance between Bozburun and the tip of the northern gulf is about 100 km (62 mi). But, the distance between Bozburun and the tip of the southern gulf is only about 30 km (19 mi). To the southeast of the peninsula, Lake İznik is situated.
The peninsula is actually a part of Samanlı Mountains, a mountain range lying between Bolu Mountains and Bozburun. The peak of the mountains within the peninsula is Taz Mountain with an altitude of 921 m (3,022 ft). The mountains are covered with forests.