Castle Eden Dene is a Site of Special Scientific Interest and National Nature Reserve in the Easington district of County Durham, England.

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.

[1] The majority of the woodland is dominated by ash, Fraxinus excelsior, and wych elm, Ulmus glabra, though sycamore, Acer pseudoplatanus is well-established and yew, Taxus baccata, is common.

The Dene is a popular venue for walkers and there are several entrances, from Peterlee and Horden to the north, Castle Eden, Blackhall and Heselden to the south, and from the A19 and A1086 roads.

To minimise accidents and to avoid damage to the plants and the dene itself, Natural England advises walkers not to stray from the paths and prohibits the use of bicycles and motorbikes within the reserve.