This is a place I had wanted to go back to as Blessington is one of the more accessible wicklow towns from my base. This route (or at least the first half of it) is less well trodden and makes a loop rather than the more customary out and back from this startpoint. It is described in Helen Fairbairn's book on the Dublin and Wicklow Mountains.
To the north of Mullaghcleevaun, west of the cleft on its north east side which contains the elusive Cleevaun Lough, is a grassy spur which veers north westerly downhill into slopes cloaked in deep heather, before reaching a stream and forestry.
This route takes a clockwise journey from Ballynultagh Gap car park to the base of this spur and follows it upwards over the more challenging heathery terrain towards Cleevaun Lough, before returning over the much easier and direct route towards Biilly Byrne's gap and then onto Black Hill.
The route follows along forest tracks initally eastwards and then southwards. Careful review of these tracks is recommended to avoid a wrong turn.
Before the forest track finally veers westward (to no particular destination), a rusted gate presents itself at O0606709162. Now you're challenged to tackle trackless wild ground. Eventually the slope does relent and the walking is easier. A more easterly bearing will take you towards Cleevaun Lough, though it is easy to be drawn closer to the summit ridge.
On a cold dry end of winter day, the grassy sections were easily traversed, but expect wet ground in summer.