If you refer to someone's inner sanctum, you mean a room which is private and sometimes secret, where they can be quiet and alone.
例句
His bedroom's his inner sanctum.卧室是他的一方净土。
N-COUNT
(寺庙、清真寺的)圣所,圣殿
A sanctum is the holiest place inside a holy building such as a temple or mosque.
英汉词典释义
n.
(寺庙或教堂的)圣所
the sanctum in an ancient temple古代寺庙中的圣所;内殿My presence in his sanctum was evidently esteemed a piece of impudence too shameful for remark.我在他的圣地出现，显然被他看作是羞于提及的莽撞事情。
<口>私室
英英词典释义
Noun
1. a place of inviolable privacy;
"he withdrew to his sanctum sanctorum, where the children could never go"