For the Puzzle Door at the Bard's castle, you have to press 10 of the panels exactly once:
Press all four cards in the 2nd row exactly once (in any order). Then press only the middle two cards of the 3rd row. Then press all four cards in the 4th row.
the door that's locked
go to the secret door
In the palace the right door
you have to finish the puzzle then click on the door
you want to arrow the door on top of the castle
the guy at the door fives it 2 you
use the rope and tjhe code dh h husfvbsufhsuiecdfhf
You have to find the key. (see the related question below)
find a way to
You go through the puzzle door and beat Mordred. (see two related questions)
Into the castle. To follow him, you have to solve the puzzle door. (see the related question)
The door to Mordred's secret underground laboratory is under the two hay bales near the mill. (see related question)