A ring of coastal mountains surround low plains at the centre of the island. The highest of these is Carrauntoohil () in County Kerry, which rises to above sea level. The most arable land lies in the province of Leinster. Western areas can be mountainous and rocky with green panoramic vistas. River Shannon, the island's longest river at long, rises in County Cavan in the north west and flows through Limerick in the mid west.