If you want to avoid the A66 from Penrith you could go out from Penrith to Greystoke then along through Motherby - once you get to the A66 you will find that you can ride on the old road to beyond Troutbeck Moor, then cross over and you can use it again to Scales before a short stretch down the pavement (cycleway) and back on to the old road to Threlkeld. Through the village, cross over again and up past the Stone Circle at Castlerigg to drop in to Keswick from there. It always surprises me when I see cyclists on the main road here when there is such a good alternative. But the back of Skiddaw route is better, perhaps 2 hours to Keswick? One word of warning though some of the hedges are being cut around here so look out for thorns etc on the road - a lot of the back roads they never seem to bother clearing them up.