I've always kind of wondered what happened to these crowns after the Pevensies went back through the wardrobe. Did they appear back in Cair Paravel? Did they just vanish? Did they get transported to Aslan's Country? I don't know. :)
"The Lamp-post was a major landmark in the country of Narnia, located in the north-western area populated by Dryads and Fauns, which was named Lantern Waste after it. Resembling a London streetlamp it stood in the middle of the forest and shone day and night. It was at the lamp-post that Lucy Pevensie first met Mr. Tumnus. He tells her that the lamp-post marks the beginning of Narnia."