Astonished researchers catalogued the impenetrables found beneath the glacier.

The impenetrability of the fortress walls discouraged any thoughts of a siege.

The explorers stood before the impenetrable jungle, unsure how to proceed.

Everyone knew him as an impenetrable, someone who never let coworkers into his private world.

The library's ancient manuscripts were impenetrably bound, their secrets sealed away from curious hands.

Engineers hoped the high-frequency waves would impenetrate the concrete to detect hidden voids.

The impenetrabilities of the ancient fortress, the dense literature, and her guarded silence each presented a different barrier to understanding.

The impenetrableness of the fortress walls gave the villagers a rare sense of security.

The new polymer coating impenetrates the fabric, creating a waterproof barrier.

After the engineers reinforced the vault, it remained impenetrated despite multiple attempts to break in.