21B Cairn William
Park at the car park at NJ663153 where an unmarked track heads NNW to meet the forest road at NJ659160 where you turn right (E). There are many biking tracks in the area, one of which heads N from NJ663162 and another slightly longer one on a forest road from NJ664161. Both lead to the col between Cairn William and Pitfichie Hill where a long zigzag track leads to the summit. It would be possible to shortcut some of these but it would be hard going.
For a short route back head SE initially on heather and then through well spaced forest and grass to meet the forest track at NJ660161. There are traces of a path which might have been a direct ascent before the bike tracks were created.
(1 hour 30 mins, 4 miles, 1100' of ascent)