What are all these plaques with triangular indentations for?


Hint 1 of 8:
They are guides to all of the exhibits in the museum.

Hint 2 of 8:
You need to find the key to activate them.

Hint 3 of 8:
As you're entering from the tapestry, it will be at the far end of the first
hallway in the museum, on your right side.

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