You actually don’t need the instruction that solving this puzzle gives you anymore, because you discovered the thing you needed to do on your own, but in case anyone else is wondering about the mural, a hint:
Note that it says UNDER US, not, say, UNDER HERE.
Or more explicitly:
You have to look under each of the individual items depicted.
As for my status, I made Encorm give me instructions for how to get to the Xanthous Chamber because she’s much better at block-pushing puzzles than I am, but the knowledge that most of what I’m going to be doing is more block-pushing puzzles is making it hard to find motivation to continue, so I might not.