The switch in the dungeon opens the back gate to the cell. Later, you can enter that way through Mordred's underground laboratory.
(see related question)
Still in the dungeon. Either the hole is too small, or he doesn't like dirt caves.
Pick up the moldy cheese, and flip the switch on the wall (it opens a back entrance into the cell). (NOTE : once you do these, you cannot get back into the dungeon through the library. If you cannot find another way in, see the related question.)
You need to flip the pieces until all the tiles form a complete picture.
At the Binary Bard's secret planetoid, entering the castle requires you to flip over 20 "cards" or puzzle sections to reveal a hidden picture (and enter the castle). For the solution, see the related question.
To solve Mordred's puzzle and enter the castle, press each of the four cards in the second row (once), each of the four cards in the fourth row, and the middle cards in the third row.
You have to click 10 of the cards exactly once each to flip them all over :all four cards in the 2nd rowthe two middle cards in the 3rd rowall four cards in the 4th row
Flip the switch
To flip over all the panels, press the following 10 panels exactly once each :all four panels in the 2nd rowthe middle two panels in the 3rd rowall four panels in the 4th row
Solve the puzzle door. It is fairly easy : push each panel in the second row once, each panel in the fourth row once and the two middle panels in the third row. This will flip all of them over.
Here is the motor switch code. You flip the first switch to the middle, then you switch the middle switch all the way to the bottom, the on the last switch you flip it down to the middle again. middle,down,middle
Yes, and one that becomes obvious with experimentation. There are 10 panels that you have to press exactly once each : All four panels in the 2nd row, the middle two in the 3rd row, and all four in the 4th row.
To open the passageway, flip all the puzzle pieces. The method is: Click once on each of the four cards in the 2nd row. Click once on ONLY the two middle cards in the 3rd row. Click once on each card in the 4th row.