1.   Somewhere in the impenetrable blackness was a desperate man, cold, hungry, hunted.

2.   But, although Robert strained his eyes against the glass, he could see nothing but impenetrable blackness beyond the hectic yellows and reds cast by the candles.

3.   For the past half-hour she had been feeling distinctly uneasy as the ever-present shadows had deepened into almost impenetrable blackness.

4.   In other years, John felt anxious sitting by himself so close to the impenetrable blackness of a mountain forest at night.