It's all dark outside.

It's totally dark outside.

It's pitch black outside.

Source: Tatoeba

On entering a dark tunnel, we could see nothing.

Source: Tatoeba

Suddenly everything went black and I lost consciousness.

Source: Tatoeba

It is pitch dark.

Source: Tatoeba

It was a dark night, with no moon.

Source: Tatoeba

You wake up lying on the rocky floor of a dark cave. A little light filters down from above. You can just make out a couple of openings leading away from the cave. What do you do now?

Source: Tatoeba