Ok, so my bad, I told you the wrong thing. The ledge you need to drop down to is actually further back nearer to the first bonfire. Just light a torch and follow the ledge to the left outside the bonfire and you'll see it. And fyi, that was not even close to the last giant. Those guys are -blam!-ers. Fighting both at the same time is suicide. You have to lure one out and kill them one at a time. But don't even bother with it now, you won't have to bother with it until you get to Vendrick, but that's a different topic altogether.