Sanctum sanctorum(noun)
(Lit- the holy of holies in the Jewish temple./Fig- a very private or highly secret place or area of activity/ a place of inviolable privacy)
Hindi meaning:गर्भ-गृह/निजी कक्ष
Synonyms: Secret Place, Confidential Place, Sub Rosa Area
Antonyms: Public Place, General Area
Example: Area 51 is sanctum sanctorum of USA.
Trick to remember: Saint rahte hai Sanctum sanctorum me. 
