From the Notes of Nikan Shrubcover, concerning the Black Tower

There have been numerous reports that as you approach the Black Tower, your mind gets foggy, and you can’t think straight. I’m not sure if this is a property of the tower itself, or due to the presence of Zaphon, or even the result of some dark ritual that he cast over the tower. If the Black Tower really is made from the remains of Darkness, the building itself may have strong arcane properties that muddles the mind. The other two theories are equally plausible; however, I tend to lean toward the Black Tower being built from the ruins of Darkness due primarily to the fact that the building material is so foreign to the area. One thing is certain, however, regardless of the cause, the Black Tower radiates pure evil.