It is 13-mile ( 20-kilometre ) square-shaped peninsula . It is bounded by Morecambe Bay to the north , the Ribble estuary to the south , the Irish Sea to the west , and the Bowland hills to the east . It is roughly a 13-mile ( 20-kilometre ) square-shaped peninsula , bounded by Morecambe Bay to the north , the Ribble estuary to the south , the Irish Sea to the west , and the Bowland hills to the east .