You have to have completed the desert laser first.
Map
Desert Obelisk
North #6
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This puzzle is not on the outside.
You can find it at the bottom of the desert temple.
After you have activated the laser of the desert area, go under the elevator on top of which the laser is and look up,
Complete spoiler:
You now know roughly where it is...
Roll over each black area below for hints.
Each new hint gives away more than the previous one.
You need to look up to see it.
This puzzle is harder to find than to solve.
Prerequisite for solving:
Hints about the location:
Show hints
Intro
The fun part here is to find the location of the puzzle.
THE WITNESS - ENVIRONMENTAL PUZZLE HINT GUIDE