Just to be sure it's not me doing something wrong, here's the walkthrough:
2- STATUE ROOM:
Now head southwest into a room with a number of statues and two secret doors. Two of the statues can be rotated. Activate the lower statue by rotating it to open the door to a bedroom that leads off the round room where you entered. You will get a message that says: The halls resonate with the sound of grinding stone. A door has opened somewhere nearby". While here also check out the pedestal at the far end of the room for loot, be careful its trapped and locked but contains a pearl, 346 gold pieces, four potions of healing, an antidote potion, a scroll of Greater Malison and five scrolls of Haste. Now head back to the NE and find the bedroom you just opened (we'll activate the other statue to open the Practice Chamber room later).
So far so good.
Colored Rune Stones: In this room you will find three colored rune stones. As you enter the room two more secret doors should be outlined in red. Neither will open at this juncture. In the center of the room there is a seating area with a chest. Open it and retrieve the red rune stone. As soon as you do this a secret door opens to the SW that leads back to the statue room. A figure appears in the corridor behind the secret door, now open, who is identified as Durlag Trollkiller. Don't be fooled. Durlag is long dead, so this must be a doppelganger. Get ready for a fight because as soon as the figure finishes his dialog he transforms into a greater doppelganger and launches a fireball into the room. Pummel this cretin and retrieve a diamond off its corpse. Be prepared for more doppelgangers in disguise on this level. Now you can enter the secret passage and pick up another book off the floor that reads:
�Foul mimic of the mortal man; �T was in my shape they killed Islanne'.
Now on either side of the bed you will find chests each containing another colored rune stone, one orange and one green. When you pick up the orange rune stone you should hear the Practice Chamber Room door open. If not, we can open it with the other gargoyle.
Also in the room is a locked closet containing an Adventurer's Robe, scrolls of Domination, Spirit Armor, Remove Curse and Monster Summoning II, Darts of Wounding, Darts +1 and Bullets +2.
Yep, door to the opposite room opens upon taking the stone.
4- SPARRING CHAMBER ROOM:
Getting In and Disarming the Traps: The doors to this chamber are opposite those of the bedroom leading off the round entry room. Do not enter at this time as the floor has seven closely packed traps and another doppelganger is waiting to ambush you. Rather, take your party back to the gargoyle room where the secret passage door should now be open as well. If not, you can open the main door by rotating the upper gargoyle, but notice when you do this that the doors to the bedroom simultaneously close.
No, it isn't open, neither does using the statue work. Nothing happens, and there's no doppleganger in the room either. No way to open any stupid door except for those already used.
...now I remember why I didn't like TOSC in the first place.