WHAT DO I DO ABOUT THE KEYPAD IN THE TUNNELS?

More unlabeled keys!

Without numbers or letters, it must be their position that's important.

You may have seen a configuration like this (a 2x2 square) somewhere already.

No, not the knight tapestry. Good guess, though.

Go to the parlor.

Look closely at the chess set.

You'll need one more clue. It's close by.

Open the bottom drawer in the parlor to find a scrap of paper.

If you need a hint on how to read this, maybe your mirror self knows. Have you tried talking to the mirror yet?

N means knight, R means rook, B means bishop and K means king.

Exactly the pieces on the chessboard, as it happens.

The note is telling you that you need to press the key corresponding to the square the knight is on first, rook second, etc.

Tap the bottom left key, then the top right key, then the bottom right key, then the top left.