In one corner was a dark hole closed by a gate: a secret passage from the house to a ruined monastery, a mile away--so we were told. My uncles had once been down some distance, but the air got bad and they came back; the gate had been put up to prevent others from trying it and losing their senses. Come to think of it, they were probably teasing us, and the hole led to the bottom of the garde-robe--which is a polite name for a medieval earth closet.
...and "earth closet" is a polite name for a latrine, which is a polite french name derived from lavare, "to wash".
I'm sure Graves was clever enough to have written that on purpose.
I am also never more jealous than when I read of privileged children having old castles to tumble around and explore. I want that childhood. Makes me want to tunnel out some secret passages in my back yard for my boys to discover some day.