Mindanao is the second-largest island in the Philippines at , and is the eighth-most populous island in the world. The island is mountainous, and is home to Mount Apo, the highest mountain in the country. Mindanao is surrounded by four seas: the Sulu Sea to the west, the Philippine Sea to the east, and the Celebes Sea to the south, and the Mindanao Sea to the north. Of all the islands of the Philippines, Mindanao shows the greatest variety of physiographic development. High, rugged, faulted mountains; almost isolated volcanic peaks; high rolling plateaus; and broad, level, swampy plains are found there.