I was getting very deep into Alum Rock Park. On the side of a culvert adjacent to Penetencia Creek, I stumbled upon, and almost in, a demonic stairwell leading to what was most likely a temple or dungeon belonging to the un-dead creatures. It was blocked off at the bottom.
Park officials describe it as "one of 27 natural mineral springs in the area - containing seven different minerals." I doubt that very much. A puddle of foul soup at the bottom of the stairs resembled bichloride of mercury with ground up wolfsbane. Probably left there by the un-holy albinos to poison dogs or foolish people.
Urban legend? I don't think so. I walked over to a stinking well.