Get to the Cemetery

The key to the cemetery gate is in a small room on the West side of the Middle floor.  Leave the stair area via the passage to the North and go through the door to the West.  Go through the next door (South), then head West as far as you can - there are 4 doors on the way. Now move South and go through the door on your right (West).   The key is on top of the tomb.

You can also get to this room from the East side of the stair area. In this case you need to turn South, then keep going West as much as you can - go North when you are unable to go West.

The locked cemetery gate is in the East side of the North wall of the castle.  It can be reached from any of the doors round the Ground Floor central stair area, although it's a very long way round from the West door.   If you choose the East door or the South door, head East until you come to the chapel.  Leave the chapel via the North door, turn left, and open the door on your right.  You can see the cemetery gate straight ahead (North).  If you choose the North door, head East  when you can;  you will eventually see the cemetery gate to the North.