Lanao del Sur is a province of the Philippines located in the Autonomous Region in Muslim Mindanao (ARMM). Its capital is Marawi City and borders Lanao del Norte to the north, Bukidnon to the east, and Maguindanao and Cotabato to the south. To the southwest lies Illana Bay, an arm of the Moro Gulf. Found in the interior of Lanao del Sur is Lanao Lake, the largest lake in Mindanao, where the Maria Cristina Falls, the largest waterfall in the country is located.