Aye mate its a canny walk, but a pleasant one, you can either park at i normally park at Craster and walk in from there, but you can park at Embelton and walk in from the north. Once you reach the castle, go through the main gate, if the national trust people are still in the little office i normally pop my head in and let them know where im going or give them a wave on the way past, chances are though if your going on an evening they will be closed. Once you in the castle head north till you hit the castle wall them follow the wall around untill you see the path cutting through the wall (heading east). You'll then come out onto the rocks/clif you can either fish from the to or walk down to the point. Casting north will get you prenty of mackerel, i find casting along the edge of the cliff produces better pollock.