Nico describes Mary Rose's island, and remembers standing with Barrie when he first had the idea for the play in 1912. See JMB&TLB p206 - or in colour in the photo gallery.
This content is elegible for transcription
It was Mary Rose Island, much the smallest thing, it has no resemblance, it is a little rocky place, it is so small, as Mary said the other day you can't tell the size these places are. But that's it. That's the island. Which I mean there is no size to it all. In other words just a little rocky place. That's what is known as Mary Rose Island. And he and I were sitting on the main land, maybe 30 yards away, looking across there, when he suddenly thought, which crystallized the idea that had been in his mind for sometime.