Begins on the buttress right of the Idwal Staircase. The scrambling starts by the stream the path crosses. Climb up a heather and rock runnel on the buttress for some distance until you reach a gully. Walk up this for a couple of metres to come out above the buttress. Head right and climb (or bypass) a small free-standing buttress then walk up to the grass couloir descending from Seniors' Ridge. High above is a quartz band; the scramble crosses this. Scramble up on rock to the right of the couloir (great holds) then trend right to gain the sloping quartz ledge. From here scramble leftwards (choice of line) to reach Seniors' Ridge.
Note that the North-West Face Route and Idwal Buttress and Continuation are the same route. The only difference is that Garry Smith describes a definite line above the top Quartz Ledge while Steve Ashton gives less detail.