Sorry, I should have mentioned that the trick of climbing the side of Dragon Spire is only for bypassing the Spire itself (at least the first time). Those doors only open from the inside (actually, the one set directly to Erathsmedor never did open for me...I think it was just a teaser so you could hear the Dragon mumbling). Of course, once you have gone through the Spire, it's an easy way to get back in from that end.