Left around 10am. Long walk up the roman road to the col below Fan Y Big, about 1 hour.
Straight up Cribyn (795), down and up to Pen Y Fan (886), and down and up again to Corn Du (873). As ever, misty on top with no view at all!
Finally along the ridge heading south, and down at the cairn to cross over the old resevoirs dam and back to the car park.
About 4.5 hours round trip, maybe 12km.

Next day we parked further along Talybont road (having got the wrong car park to start with). From there straight up to the plateau and keeping to the ridge heading north east. Then back round to Fan Y Big, and now down the roman road and back round a bit of the Taff Trail to the car pack. A bit less than 4 hours round trip -- about 11km again but only one steep climb.
This picture (taken Sunday), shows ridge leading to Fan Y Big in foreground, Cribyn behind on the right, Pen Y Fan centre, and then Corn Du and the ridge going off to the right.