I wrote it once but cannot remember where I managed to put it, so there you go:
Enter castle. Your first target would be large hall with first cube, hanging from ceiling and filled with those pesky orcs. On the opposed wall from the entrance there is a window you can jump through. Run through the hall, ignoring all nasties to this window (it is where normally pass is if you are doing all things right supposed to) and jump through it. The only important thing is jumping at right distance.
Now you are in large U-shaped hall, filled with eyes and with high structure in the middle of U. Run into left branch, and in distant 1/3 of it you will notice narrow ledge on your right, leading backwards. Climb the ledge - at the top of it there is secret door you can open and go in small room for healing. Then lead to the distalnt edge of U left branch via hallway until the end, guarded by 2-3 eyes. On your right there will be hall, filled with all kinds of Liches. Jump down and if you are lucky enough, liches would be slow enough to dispel your jump spell. You will land right near the niche with memory crystal and second cube, hanging from ceiling. Grab the crystal, run to the plague in wall, hit it and hit the cube from ceiling - you will be teleported to the room with Lich Book. Destroy it, then run out.