Well, there are 3 optional rooms in the maze that are the ruins you explore in chapter 4, and one of them has the orb. It would kill all the fun to give the exact directions, but it isn't very difficult to find that room, as the way to the end of the ruins is a pretty distinct corridor. So you just need to try exploring the areas before it.
There's also a small "pattern" to the teleporters and the walls around them (and whether they take you somewhere nice or take you nowhere), so once you realize it things become pretty easy, I promise. Just stack up on potions (or just flee from the battles).
Well then, have fun! xD