Chronicles of Narnia by C. Lewis - A wardrobe leading to the kingdom of Narnia brings four children face to face with the evil White Witch and Aslan the lion-king who leads the fight against her. (Levels T - U)
I used to sit in my closet as a kid, and just wait for the day to come! Clearly it was the wrong closet haha and I had an old wardrobe in my room, no lie. Can't tell you how many times I tried to find Narnia.