The Lamppost of Lantern Waste was created at the birth of Narnia. Jadis threw a broken iron arm from a London lamppost at Aslan, and it bounced off of him and fell to the ground. Due to the fast growth of the new world, the iron bar took root and grew into a fully-working, independant lamppost.
When the Wardrobe was used as a portal into Narnia, it's entry was near the lamppost, and it was one of the first things Lucy saw on her first trip into Narnia. Later, the Pevensies see the lamppost before stumbling back into England. It was near the lamppost that Dr. Cornelius found Susan's lost horn.