This viewpoint, high above Derwent Water, can be reached from the very narrow road that goes to Watendlath Tarn just south of Keswick. Be aware that it is very narrow and you'd have problems getting there with anything larger than a regular sized vehicle.
There is no sign although it is marked as a scenic viewpoint with parking on the Ordnance Survey maps of the area (and on Streetmap.co.uk.
We found it while looking for a cache in the area - appropriately called "Surprise View"