Wardrobe

History
The 'wardrobe' in the Lion, the Witch, and the Wardrobe was first seen chronologically in the Magician's Nephew, when Digory Kirke, who later becomes the Professor, had his own adventure in Narnia. Aslan sent him to get two silver apples from a magic tree and bring them back. When he did, one apple was planted right there in the ground, and a beautiful tree grew, with silver bark. The other apple Aslan gave to Digory to take home to his sick mother. When Digory returned to London and gave her the apple, she ate it and soon recovered from her long sickness. On impulse, Digory planted the apple core in his back yard, and it soon grew into a tree as well - a sister tree to the one that had grown in Narnia. It is noted in the book that sometimes the apple tree would creak and move as if being blown in the wind - when there wasn't any, as if it could feel the winds that blew it's sister tree.

Portal to Narnia
Eventually, the tree was blown down in a storm, and Digory - then much older - had the wood from the tree made into a beautiful wardrobe. This was placed in a small and otherwise empty room in his large country home, where many years later Lucy Pevensie discovered it during a game of hide and seek. Hiding inside it, she felt tree branches and snow, and looked up to find herself in Narnia. Soon after the other three children followed her, and saved the whole country from the White Witch. They came back through the wardrobe the same way, and told the Professor about all of their adventures. He warned them not to tell anyone, and that they would never get to Narnia again - through the wardrobe anyway.

Inspiration
Author C. S. Lewis had an English country home of his own, and he took in children who were fleeing London because of the German air-raids much the same as the Professor did. He also had a magnificent wardrobe in an upstairs room, said to have been of particular interest to one little girl, and to have inspired the wardrobe for Lewis is now known.