Rockabill consists of two small, low-lying, granitic islets situated c. 7 km off the coast. The islands are separated by a narrow channel though are connected at low spring tides. Rockabill was built in 1860, can be viewed from all parts of the coast of Fingal. It is the largest breeding site in Europe for the now rare Roseate Tern. A permit is required to visit Rockabill.