Thanks Beck. I was there quite accidentally really - I was looking for information about something else entirely and heard about a Cold War research group going, and looking for a fourth person to make up the party. It seemed like such a bizarre thing to do, and also not the kind of opportunity that arises every day, that I was compelled to sign up...
Oh, I don't know if it's clear from the photo, but that gasmask was tiny - obviously for a very young child, which makes it a bit creepier.
Cheers Gordon! Praise from Caesar indeed.