The highest mountain is Mount Apo. It measures up to above sea level and is located on the island of Mindanao. The Galathea Depth of the Philippine Trench in the Philippine Sea is the deepest point in the country and the third deepest in the world. The longest river is the Cagayan River in northern Luzon, measuring about . Manila Bay, upon the shore of which the capital city of Manila lies, is connected to Laguna de Bay, the largest lake in the Philippines, by the Pasig River. The Puerto Princesa Subterranean River, which runs underground through a karst landscape before reaching the ocean, is a UNESCO World Heritage Site.