it's cool that there's an entire subgenre of Doctor Who stories that are "what if there was a castle and it had some sort of infinite recursion shit going on that would that be fucked up or what"

also, after watching Castrovalva it feels really obvious what an influence Bidmead had on Rob Shearman. I think there's a direct line you can draw from Castrovalva to The Holy Terror then, I'll bet, to Heaven Sent.