I walked the full east wing today while everyone was out. Systematically — every room, every corridor, checking the places I hadn't checked before.
I found: a narrow cupboard with a false back that opens into a crawlspace (not large enough to be useful but noted); a panel in the east corridor that gives slightly under pressure and is definitely covering something; and, in the rear garden wall, a crack about half a metre long and wide enough to fit through sideways.
I'm not planning to go anywhere. I just like knowing the shape of things.