Turns out those walls they found aren't just walls. They're the ruins of an ancient castle.
In fact, the place reminds Peter of their castle of Cair Paravel.
It grows dark, so exploration must be put on hold to build a campfire.
They build it in the safe corner of two walls and have a supper of warm apples. Make sure to save room for a dessert: cold apples.
After dinner, Susan goes to have a drink at the well. She returns with a golden chess piece she found. The others miss Cair Paravel, but Peter informs them that—wait for it—that's exactly where they are.
But wait a second, Edmund says. Cair Paravel wasn't on an island, and a year isn't enough time to make a palace a ruin either.
Lucy reminds them that a door should be nearby if this is indeed their castle.
And wouldn't you know it? Under vines and overgrowth, they find just such a door.
Despite Susan's initial fears, they break open the door and head down the stairs. There, they find the treasure chamber filled with all their trinkets and goodies.
Looks like they're back.
Because Edmund's torch (read: flashlight in American) runs on batteries, and Narnia doesn't have any RadioShacks handy, they decide to grab their Christmas presents and leave.
Peter finds his sword and shield, Lucy her magical cordial, and Susan her bow and quiver. Susan's horn is missing, but she still makes out better than Edmund as the poor guy didn't get a Christmas present—though it was kind of his own fault.
They spend that night on the hard and uncomfortable ground, but fall asleep all the same.