First time was in about 1971/2 as a young lad, trailing exhaustedly after an ex SBS Royal Marine Commando, who although in his 50's (as I am now!) could still put in a good day in the hills.
Second time was via a 670ft v.diff rock-climb 'Avalanche Buttress' - on a Craig yr Ysfa, a remote crag at the back of Carnedd Llewelyn. We completed the rock climb up onto the top of Llewelyn, before traversing the range and descending to Ogwen, from Pen yr ole yr wen.
Twice from Drum to Ogwen Cottage, once up via Amphitheatre buttress
Only climbed here a few times and the weather's always been bad. Will have to make time to return.