[As written] Milldown is probably a corruption of the Gaelic Meall Donn meaning Brown Hill.
The Rhinns of Kells (a rhinn is a point or promontory and Kells is the name of the parish) is the easternmost of the three main ridges of Galloway Hills, the others being the Dungeon hills (including Craignaw and Dungeon Hill) and The Awful Hand (including The Merrick).
The ridge traverse is a popular outing for hillwalkers, with the highpoint (Corserine) giving excellent views over much of Galloway. For climbers, the corries on the east side of the ridge occasionally hold ice and snow in sufficient quantities to form some good routes. Climbs have been recorded on Milldown, Millfire and Corserine, though Milldown has the highest concentration of good routes so is the only one included here – see SMC Lowland Climbs for details of the others. The crag is split into two corries by the North-East Ridge, which is evident on the 1:25k map.