Never been to that specific one but I've done a fair bit of work in derelict hospitals and sanatoriums over here in the UK and they've got a completely different energy to other abandoned buildings. Hard to explain if you haven't felt it. Something about the layers of distress in those places I think.
From what I've read about Millbrook it had a pretty grim history even by sanatorium standards. The isolation ward stuff especially. If you're doing remote viewing sessions there or EVP work I'd genuinely be curious what you're picking up on the upper floors, thats where I'd expect the residual activity to be concentrated based on what I've seen in similar locations.
Anyone actually been inside or is this more of a perimeter job? Would help to know what access is like before this thread goes too far down one road.