Ah.I think there's something ominous here that Eldingar's not picking up 'cause he's an apex predator shut in so hasn't had his danger sense developed at all. The whole reference to "dark, festering, unforgotten" and the capped well outside lean towards the idea of something tainted, corrupted and toxic being stored out of sight. The water so dark it looks more like oil than anything. The sealed shit near an isolated wizard's watchtower a million miles from anything that could open it. It really evokes the idea of Bad Shit.
So this might be the home of Lich Husbando.