This game was made for the Apple //, the Commodore 64 and the IBM PC on a single disk. Most folks get very frustrated by this game simply because they don't pay attention to the graphics and what is shown. Also the clues are there, but they are very hard to figure out with a complete walkthough of open areas in the area.

@billy: I've never seen any mention of this for the C64. Do you have any additional info?

There was an Apple // and IBM PC version and there was a VERY RARE version for the C64. My buddy had it in the 80's for his C64/C128/Amiga 1000. I have no proof and have not seen him ever again. Wish I could find more about it!
Here is the link for an image to the Apple/IBM disk version. This site is AWESOME!
http://mocagh.org/loadpage.php?getgame=demonforge

Very much in the tradition of old Sierra adventures, but better designed. This game is often accused of being too obscure and hard, but I think it's par for the course. It's not for beginners and requires the player to stay sharp, but puzzles are fairly logical. There is only one really involved puzzle (the staves room) but there are enough contextual clues to notice the pattern. I personally found the evil bridge and balls puzzle trickier. Try this one if you fancy old-school linear escape-type adventures.