Get in a hovercraft and drive up the road to where you were previously able to do the seamwalking to get up the cliff.
After driving up the hill, go forward until you get to the close spot where the walls almost meet.
Turn the hovercraft so part of it is on the other side, then moved to your left.
If done right, you will drive up on the wall and turn around and land on the other side. Then, just drive to the cliff and drive up it with your hovercraft.
Get out, and run up and you are out.
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