Can anyone give me a tip how to use this key to operate the mechanism at the base of the tower in the main square, please? I have tried to position the three teeth to match the shape of the slot in each of the stone bars, but I can't seem to get the correct configuration.
This is still quite early in the game, I think, so I am at an early stage in getting into the right mode of thinking for this game.

For anyone else having trouble, the important part is...

[spoilers]the little pin on the stone tooth of the lock mechanism. That corresponds to the large fixed projection on the key. When looking at the key from the tooth side, orient the pins based on the opposite of what the keyhole looks like.[/spoilers]