Prince Caspian and the Voyage of the Dawn Treader (1989)

Young Prince Caspian of Narnia wonders and dreams about the old days of Narnia when animals talked, and there were mythical creatures and four rulers in Caer Paravel. But his uncle and aunt don't like to hear him thinking of such things, and plan to murder him and take his throne. Caspian's tutor, Dr. Cornelius manages to save him, and not only teach him about the old ways, but bring him into the real Narnia and introduce him to the real Narnia. But Caspian's plight is desperate, and he must use the legendary horn to call help from another world: Peter, Susan, Edmund, and Lucy.