Never been myself but Pennhurst has been on my list for ages. Seen some of the EVP recordings that have come out of that place and a few of them are genuinely hard to explain away.
The history there is obviously grim which i think does something to a location, not sure what exactly but places with that kind of suffering attached to them tend to produce more activity in my experience. Did a session at a former workhouse near Bristol a few years back and picked up some of the clearest responses ive ever got.
Would love to hear from anyone whos actually done an overnight there. Did you use any equipment or just go in blind? And was it the main building or the outbuildings where you got the most activity? From what ive read the colony farm area gets overlooked but sounds promising.