Shadowheart

[she can just kinda thoughtshare this thing.]

It is a portal to a section of the astral plane - I think it was being used as a prison. I'm not sure I could explain exactly how it works, but there's a spirit inside and it offers its protection over us. The spirit is not trustworthy exactly, but better than assimilation.

[this isn't accurate but she is like two short rests too early to be able to explain it.]