impenetrable

adjective
1
that cannot be entered, passed through or seen through
غیر قابل نفوذ, نفوذ ناپذیر, رسوخ‌ناپذیر
opposite penetrable
2
impossible to understand
غیرقابل‌درک, غیرقابل‌فهم
an impenetrable mystery
Her expression was impenetrable.
Their jargon is impenetrable to an outsider.
synonym incomprehensible