@slarstorm You need to use the javelin and the artifact in combination to reach the top.
Related spoiler-ish question:
I don't get the reason behind the 4 pods at the top of the mountain. At first I thought they were the landing pods for the stellanite golems, but weren't there only 3 golems (not including Billy, who crashed his pod in the Duri forest)?
NTT
Just read the guide - found the answer