Animal Frenzy
The evil of this place seems to have faded, dropping for a cloying stench down to a displeasing, lingering feeling. It will fade over time, just making the place unpleasant for anyone staying here.
There's little to identify who this tower belonged to, but you can guess a few things. First, they haven't come here in a very long time, likely longer than any of you have been alive. Second, they didn't plan on leaving. There's just too much material left here. Third, their research is extremely specific and unusual. If anyone knew of it, it wouldn't just be in a city, it would have to be a wizard's college, and even then they would be unlikely to know much about it.
Flying over the area, Spriggy does spot a pond that seems tainted. At least, judging by the red-tinged plants surrounding it. It's much more diffused than the plants surrounding the tower, though.