4818  A ring of coastal mountains surround low plains at the centre of the island . The highest of these is Carrauntoohil ( Irish : Corrán Tuathail ) in County Kerry , which rises to 1 @,@ 038 m ( 3 @,@ 406 ft ) above sea level . The most arable land lies in the province of Leinster . Western areas can be mountainous and rocky with green panoramic vistas . The River Shannon , the island 's longest river at 386 km ( 240 mi ) long , rises in County Cavan in the north west and flows 113 kilometres ( 70 mi ) to Limerick city in the mid west . 