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.

Hint 6 of 8:

In a few cases, the key will also have a more tangible effect.  Read on to
find out about these.

Hint 7 of 8:

There is one plaque that appears to be detached from any exhibit.  It's in
the middle of a hallway, next to a bulge that makes a small room.  Use the
key there to get your first "speaking stone".

Hint 8 of 8:

Use it next to a giant blue crystal.  Flames will light in the room when you
do.