Ireland's central lowlands of flat rolling plains are dissected by bogs, loughs (lakes) and rivers, and surrounded by hills and low mountains. The major mountain ranges include the Blackstairs, Bluestack, Comeragh, Derryveagh, Macgillycuddy's Reeks, Nephinbeg, Ox, Silvermines, Slieve Mish, Twelve Pins, and Wicklow. The country's highest point, Carrauntuohill, in the far southwest, stands at almost 3500 ft high. The western coastline includes numerous sea cliffs. The most famous, and some say the most beautiful in all of Europe, are the Cliff of Moher. They reach a maximum height of just over 700 ft. Ireland has dozens of coastal islands, including Achill, the country's largest. Others of significance include the Aran Islands to the southwest of Galway and Valentia Island just off the Iveragh Peninsula. Other peninsulas of note include the Beara and Dingle. The River Shannon at 240 miles long is Ireland's longest river. It widens into four loughs along its route, including Lough Allen, Lough Bafin, Lough Derg and Lough Ree.