I managed both at last. I have never found any of these caves before (thats why I was more confused). I haven't explored as much as I should of it seems. I first got there ok with Arokh and then tried on my own. I was lucky, jumped neatly on the platform on first attempt
The valley one I was in the wrong place too. I was literally on the bottom surrounding (behind the actual building) which is where I went wrong. Arokh managed to sit on it there eventually, but also sat through the brick bit, heh. Anyway, I went to the snow bit, landed fine and after a few minutes he went through perfectly. I decided to try it again and it took me 20 minutes that time to get right, but I got through by turning Arokh around a bit.
Thanks for the help again. I must say I was disappointed by the first to find it was only a cave opening. I was expecting a weird door by the way she explained it.