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.

Hint 4 of 8:

The skeletons don't seem to like it when you take the key, and they'll try to
steal it back from you.  You may have to fight them if they catch you with
it.

Hint 5 of 8:

Put the key in the indentations, and you'll learn about the exhibits.