Wood Between the Worlds

The Wood Between the Worlds is the name given to a common access portal allowing travel between many different worlds, Charn, Earth, and Narnia being the only ones we know about. It had the form of a quiet forest dotted with many wide pools of water. Each pool was a portal to a world, and jumping in transports a person to that world. This was the first means of access to Narnia. It was used by Digory Kirke and Polly Plummer to go first to Charn, then return from Charn to Earth with Queen Jadis, then take Jadis, with Frank, Strawberry, and Andrew Ketterley, to Narnia.

Travel between worlds
In order to use the portals, a person must be touching one of the magical rings made by Andrew Ketterley, Digory's magician uncle. The rings are of two types. Green rings transport a person from a world to the Wood. If a person on Earth touches a green ring, for example, he will disappear and appear in the Earth pool in the Wood. The yellow rings transport a person out of the Wood to a world. If a person in the Wood wants to go to Charn, for example, he steps in the Charn pool while touching a yellow ring, and materializes on Charn. How the location at which one materializes is chosen, is not clear.

Contact with the ring must be by skin. Another feature of the rings is that the effect works like electricity, by chain of contact; you don't have to be touching a ring, merely touching someone who is touching one.

Neither Uncle Andrew, who made the rings, nor Digory and Polly, who were tricked by Andrew into being guinea pigs and trying them out, understood any of this. This resulted in Digory and Polly blundering into Charn, then accidently transporting Jadis with them back to Earth by the 'chain of contact' effect when she grabbed Polly's ear as they were leaving. The next time they used the rings, to get Jadis off of Earth, they understood them better, and used the 'chain of contact' effect, with Digory grabbing Jadis's heel while Polly touched the ring. Unfortunately the chain of contact included Uncle Andrew, Frank the cabbie, his horse Strawberry, and even the cab, which all got transported to Narnia.

An interesting detail is that the initial choice of Narnia as a world to go to, which began all the contact between Narnia and Earth, was made by Strawberry the horse, who blundered into the first pool he saw because he was thirsty, which happened to lead to Narnia.

Access to the Wood between the Worlds was lost after Digory and Polly returned from Narnia, when they burned the magic rings so Uncle Andrew couldn't use them again.

The Wood itself
The Wood itself is not a 'world' in the sense of Charn, Earth, or Narnia. It seems to be uninhabited, which is understandable since spending time there seems to cause amnesia, and perhaps sleepiness. Digory and Polly nearly lost all memory of who they were in a short time there. Something about the evironment was toxic to Jadis, who lost her strength and vitality while there.