"Can you swim?"
"A bit. Can you?"
"Well - not much."
"I don't think we shall need to swim," said Digory "We want to go down, don't we?"
Neither of them much liked the idea of jumping into that pool, but neither said so to the other. They took hands and said "One - Two - Three - Go" and jumped. There was a great splash and of course they closed their eyes. But when they opened them again they found they were still standing, hand in hand, in the green wood, and hardly up to their ankles in water. The pool was apparently only a couple of inches deep. They splashed back on to the dry ground.
"What on earth's gone wrong?" said Polly in a frightened voice; but not quite so frightened as you might expect, because it is hard to feel really frightened in that wood. The place is too peaceful.
"Oh! I know," said Digory, "Of course it won't work. We're still wearing our yellow rings. They're for the outward journey, you know. The green ones take you home. We must change rings. Have you got pockets? Good. Put your yellow ring in your left. I've got two greens. Here's one for you."
They put on their green rings and came back to the pool. But before they tried another jump Digory gave a long "O-ooh!"
"What's the matter?" said Polly.
"I've just had a really wonderful idea," said Digory. "What are all the other pools?"
"How do you mean?"
"Why, if awe can get back to our own world by jumping into this pool, mightn't we get somewhere else by jumping into one of the others? Supposing there was a world at the bottom of every pool."
"But I thought we were already in your Uncle Andrew's Other World or Other Place or whatever he called it. Didn't you say -"
"Oh bother Uncle Andrew," interrupted Digory. "I don't believe he knows anything about it. He never had the pluck to come here himself. He only talked of one Other World. But suppose there were dozens?"
"You mean, this wood might be only one of them?"
"No, I don't believe this wood is a world at all. I think it's just a sort of in-between place."
Polly looked puzzled. "Don't you see?" said Digory. "No, do listen. Think of our tunnel under the slates at home. It isn't a room in any of the houses. In a way, it isn't really part of any of the houses. But once you're in the tunnel you can go along it and come into any of the houses in the row. Mightn't this wood be the same? - a place that isn't in any of the worlds, but once you've found that place you can get into them all."
"Well, even if you can -" began Polly, but Digory went on as if he hadn't heard her.