Chapter 15, why was the stronghold a good hiding place?

From the text:

The Stronghold made a splendid hiding place. The overhanging boulder offered ample shelter. When it was light we would gather bracken and make comfortable beds with the blankets we had brought. There was good drinking water within a stone’s throw, and, as I have told you, Sir Philip’s peel tower was only a little way down the valley. By walking half a mile we could reach a spot from which we could look right down on it.