Castle Eden Dene is a Site of Special Scientific Interest and National Nature Reserve in the Easington district of County Durham, England. It is located mostly in Peterlee, between the A19 and A1086 roads.The dene is the largest, and biologically the richest, of a series of deep ravines that have been incised through the Magnesian Limestone and overlying boulder clay of coastal Durham by streams flowing into the North Sea.