Actually it could no longer be called a tunnel mouth.

Then he saw the path, leading away into yet another dark tunnel mouth.

The face where he now worked was at least sixteen feet from the tunnel mouth.

Most of the human bodies at the tunnel mouth had been moved.

He made out the black shape of another tunnel mouth.

Lights above the tunnel mouth changed from red to green.

Again he looked down the stream at the tunnel mouth.

I leaned my head out of the tunnel mouth to get a better view.

At the bottom she could make out the shadow of a tunnel mouth.

But those who still lived of the men from the tunnel mouth were charging us.