Excalibur 2555 AD

Press [Esc] to pause the game.
Hold [F12] and press the following arrow keys.
Continue the game. A message should appear displaying the cheat.

U,U,R,R,U,U,U,U - Unlock all doors (except the room you're in)
U,U,U,L,L,L,L,L - Full Health
U,U,L,L,R,R,L,L - Max Sword Power
L,R,L,U,R,U,U,U - Level Skip
(Information from Cheat Machine)