There are two approaches to this impressive crag, both taking about 25 minutes.
Approach 1: Follow the road by the taxidermist in Llangollen (Dinbren Road) to a T-junction below the Dinbren crags. Turn left and follow the road for about 3 miles until it takes a sharp left bend at a small waterfall. Park as best as possible somewhere around this area (can be difficult). Walk back down the road from the ford for 50m to a gate on the left. Go through this and follow the well-appointed path (Offa's Dyke) through a forest and exit from it. Continue along the path until the edge of Craig Arthur comes into view. When it does a small path up the scree slope leads to the left-hand end of the crag.
Approach 2: From the T-junction below Dinbren, turn left and follow the road for 400m until a small layby on the right gives parking (below Pinfold and Monk's Buttress). Walk down the road and through a large gate on the right onto a gravel track. After 100m continue leftwards, contouring the edge of a farm, onto the Offa's Dyke path and follow this around the hillside and past the Twilight crags until Craig Arthur can be seen up and to the right. From here pick your way up the grassy hillside alongside a stream until a good path leads left to Dawn Buttress.