The Sierra Madre Mountains is the longest mountain range in the Philippines. Running in the north-south direction from the provinces of Cagayan to the north and Quezon to the south, the mountains form the eastern backbone of Luzon Island, the largest island of the archipelago. It is bordered by the Pacific Ocean to the east. The Pacific coast of Luzon along the Sierra Madre is less developed as the lofty and continuous mountains forms a bold and an almost inaccessible shore, exposed to the full force of the northeast monsoon and the waves of the Pacific Ocean. Some of communities east of the mountain range and along the coast are so remote they are only accessible by plane or boat.