Cambodia is one of Southeast Asia's smallest countries—about the size of the state of Washington. The country is bordered by Thailand to the west and northwest, Laos to the northeast, and Vietnam to the east and southeast. In the south, Cambodia faces the Gulf of Thailand, which provides access to the Indian and Pacific oceans. The coastline here is small, largely undeveloped, and isolated by a low mountain range. Much of the country is a low-lying plain dominated by the region's largest lake, the Tonle Sap, and a network of waterways forming the start of the Mekong Delta. Its northern border with Thailand is a remarkable escarpment, rising from the plains to heights of up to 1,800 feet—a natural defensive border and the site of many ancient fortresses.