Bull Island is an ever expanding slick of land in Dublin Bay. It was first formed by sand deposits in the 19th century when North Bull Wall was built to keep shipping lanes clear. It has been growing ever since, and is expected to merge with the mainland in the next 50 years. For now access is by a wooden road bridge and a causeway at Raheny. Reasons for visiting include numerous species of birds, which have led to the area being designated both a Unesco Biosphere Reserve and a National Nature Reserve.