They may have another entrance.

If so, we must find it.

In the first place, it may be easier of entry; in the second they might escape from it after dark." Again the search began.
"Do you think it is likely to be higher up or lower down, O'Connor ?" Lieutenant Desmond asked.
"There is no saying, Desmond; the passage seems to go straight in.

I should fancy above rather than below." For a long time they searched without success; then Ralph, who had gone higher up the rocks than the rest, came upon a clump of low bushes growing between some large bowlders.

There was nothing suspicious about them, and he was just turning away when he perceived a slight odor of peat smoke.
Silently he made his way down to the captain.
"I have found another entrance," he said.