Never been to Briar Hill specifically, but I've investigated a handful of decommissioned psychiatric facilities in the UK and the pattern of reported phenomena tends to be remarkably consistent across sites like these - long dark corridors, basement-level cold spots, and the classic shadow figure sightings in peripheral vision.
That last one is obviously my main interest. A few things I'd want to nail down before attributing anything genuinely anomalous:
What time of day were the experiences happening? Sleep deprivation and low-light conditions produce significant perceptual artefacts, Were multiple witnesses present simultaneously, or are these accounts being compared retrospectively?, Any EMF baseline readings for the building? Old institutional wiring is notoriously noisy - Mel-8704 or similar would give you a decent picture
The sanatorium context is interesting from a psychological standpoint too. There's a well-documented expectation bias in locations with dark histories - people go in primed to experience something, which muddies the data considerably.
That said, I don't dismiss these sites outright. Some of my most compelling shadow figure observations have come from buildings with histories of trauma and concentrated human suffering. Whether that's causal or coincidental is the question I'm still trying to answer honestly.
Has anyone done a proper overnight with consistent logging equipment rather than just a walkthrough? Would be curious what the raw data looks like.