Coney Island sits a kilometre or so south of Rosses Point in the middle of Sligo Bay. At low tide a marked road across the sand from Strandhill makes it driveable; the drive is famous and slightly nerve-wracking, with the tides giving you a fixed window each day. There is also a ferry from Rosses Point pier during the summer.
The island is small — about 400 acres — with a single pub (McGowan's), Coney Island church, a freshwater holy well, and long sand beaches on the seaward side. It can be walked end to end in a couple of hours. Check tide times carefully if driving across; cars get caught every year.