Also, those steep rocks around Intensity Bluffs. You can climb them.
There is also this suspiciously non-steep rock that you can hop your way onto (to the east of the beacon and Wolf Chasm entrance),
and walk around
the Wolf Chasm,
and then just hop in for the ending, as you have just enough health to make it from the nearby block to it,
Edit: If you go north from the Intensity Bluffs' beacon, you can similarly "walljump" out of the area and go straight for the second ending too:
I imagine that one could complete the game very quickly this way, but also loose the purpose in progress, as such walkthrough would consist almost entirely out of jogging on those lovely hills outside the map.