1. Warrior (a worn-down iron key) - from @, n, all w, n, 3w, s, w, s
2. Soldier (a large black diamond) - 6n, w
3. Go back to @, all n, unlock door e, 2e, u, s, u, w, pick door w, kill guards, use winch
4. The commander (a shiny steel key) - go back down to room before door to tower, close/lock door e, n, 2e, n, 2e, 2n, dis and kill commander
5. Grey commander (a heavy brass key) - all s, all w, s, 2w, n, unl door n, go through and lock it after. all n, pick door e, kill
6. Larenev [!dis, mage] (a large yellow diamond) - w, 2s, search, all w, 2n, search, d, find larenev, trap it, plague and kill
7. Go back up, 2s, e, u, put diamonds socket
8. Noegerat [!dis, warrior] (a dull grey key) - 3e, d, w, 2n, w, n, o door u, u, follow path south to find him [Watch out for Balcony rooms, fleeing from one might put you before oak doors. Then you will have to waste key charges to reopen/lock to get back in.]
9. Terroien [!dis, cleric] (a large hooked metal bar) - go back to staircase, 2e, n, trap, unl door w, solo in and find terroien, lure it out. Terroien will dispel your spells.
10. Brunwald [!dis, mage] (a titanium key) - go back in and follow path down to slab, unlock slab, d, find and trap Brunwald down here, kill it
11. Go back to slab and clear/sr it, do the same for the room under slab and all three rooms south of that, and finally the room west
12. From under slab, s, all w, n, u, follow path e to {Gates of Chepstow}, 2n, unl door e, 2e, u, s, u, 2w, unl/open cell, wait for Lord Chepstow to join form
13. Take form back down the tower and to west of unlocked door, n, 2e, n, all e, all n, search, d, follow path to lock door, unlock, west, d, all s, w, wait for chepstow to disappear, search, w, get all:
griffon-hide pack
griffon helm
a heavy platinum ring
a spiked belt
a silver breastplate embossed with a griffon

Locked route involves killing Skrethlechten for his key which opens a door out of the castle to the tower area. This area is locked to the outside if you followed step 4 from above. Lord Chepstow's cell can be reached using this method; however, Chepstow will need to be taken to his vault from the castle instead of the kitchen. This method is definitely more difficult because it is longer so there are more mobs in between with fire/gas rooms.

To take this route, do Skrethlechten after step 7 from above then continue with the rest of walkthrough. Of course, ignore steps 12 and 13. Instead, take Chepstow back the way you came out of the castle, up the panel hallway (Noegerat area) and to slab.

Skrethlechten [dispelable, cleric] (a cast iron key) - from {Shadowy Hall} all e, all s, w, engage Skrethlechten, lure & trap it in a safe room and kill.