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 rise to 1 @,@ 038 m ( 3 @,@ 406 ft ) above sea level . The most arable land lie 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 , rise in County Cavan in the north west and flow 113 kilometres ( 70 mi ) to Limerick city in the mid west .