This isn't Cosson Hall, but rather, one of the other buildings in that whole area.
A friend took me out here around October on a pleasant weekend afternoon. Getting in was a fun experience, we took the hard way in and discovered an easier way out.
My friend was telling me about a run-in with private security during a previous outing here, but we didn't encounter anyone else that day besides some street fashion photographers doing their thing outside.
I'm still not sure exactly what we wondered around, there were many different rooms with various themes; a classroom, machine shops, office spaces with reception, some bedrooms. Great opportunity to explore a lot of different things.
If anyone has any more history about the place, I'd love to hear more about it.
Sorry for the lack of photos, I've deleted many of the photos taken at the place and archived only a handful of them since this was a while ago. It certainly does not do the numerous sights justice.