1. the innermost or most private parts of something; the most secret or hidden recesses
Usage: formal; literary

Examples

• The archaeologists explored the penetralia of the ancient temple.
• She kept her most precious memories in the penetralia of her heart.
• The detective sought clues in the penetralia of the old mansion.
• Only trusted advisors were allowed into the penetralia of the palace.
• The scholar delved into the penetralia of medieval manuscripts.
• The cave’s penetralia remained unexplored for centuries.