There is a small car park on the A4109 in Seven Sisters at the start of the wide mine road at SN822091, but it is possible to drive a mile up the road to a ‘lay-by’ (which held a Winebego on my trip). Continue to the mine car park and turn left to follow unmarked old mine roads to the summit path at SN840077 from which the trig point is a short distance. I suspect it is possible to bike in from Dyffryn Cellwen further north.
(1 hour 45 mins, 3.6 miles, 900’ of ascent)