Randoon (Randún) is a Turgesius Viking fortress located southwest of Lough Lene in Ireland.

The fortress is situated upon a hill in Ranaghan, dominating by its height all other ringforts in the area, and overlooking Lough Lene between the towns of Castlepollard and Collinstown.

These remain today as historical relics Early Medieval Period of Ireland and Western Europe; they protected by Irish national heritage law.

The area supports deciduous woodland mostly of native species such as hazel (Corylus avellana), rowan (Sorbus aucuparia), ash (Fraxinus excelsior) and sessile oak (Quercus petraea).

On occasions the pochard population, which is one of the largest in Ireland, has exceeded the threshold for international importance (i.e. 3500 individual fowl).