Titty saw a butterfly drop on to a clump of heather growing low down in a cleft in the steep slope of grey rock but forgets the butterfly: Roger! Roger! It's a cave. It was a dark hole so deep in the shadow of the thick bushy heather ... that it would have been easy to think it was no more than a cleft in the rock ... (or) not to notice it at all (SD4).
John and Susan do not see the cave until Titty shows them the opening. John says it is all right as it is Solid rock and that It's not really so very big. And If we call it Peter Duck's Cave, then when we want to talk about it when there natives about, or enemies, we can say, 'Go to Peter Duck's' .... and no one would ever guess we meant a cave (SD12).
Susan sees a glimmer high up in the roof while she is brushing it and finds the hole through to the heather which means that the air in the cave is not bad, except for the dust. I expect people lived in it, once (SD14). Mother says what a place to hide in ... but no sleeping in it (SD15).