 A ring of coastal mountains surround low plains at the centre of the island . The highest of these is <unk> ( Irish : <unk> <unk> ) in County Kerry , which rises to 1 @,@ <unk> 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 <unk> . The River Shannon , the island 's longest river at 386 km ( 240 mi ) long , rises in County <unk> in the north west and flows 113 kilometres ( 70 mi ) to Limerick city in the mid west . 
