We found one of those when we were building our fence/woodshed, one of the fence posts got cemented in right on top of the tank. Apperently there use to be an old school right next to my house back in the early 1900s, it was probably the water cistern for that.I saw a weird brick structure, it looks like some sort of cistern or something
I hate to let something like that got to waste, so I pumped it out and cleaned it up, even tiled the floor, now I use it as a sort of cool room for keeping stuff from freezing during the winter.
Here's what it looks like now. My youngest son is the tour guide.
Oh and no witches, sorry.