Aslan's How is one of many locations created by C.S. Lewis for his series of children's novels, The Chronicles of Narnia. In The Lion, The Witch and The Wardrobe, Aslan's How is the hill on which The Great Stone Table rests.
I did not say to myself, "Let us represent Jesus as He really is in our world by a Lion in Narnia": I said, "Let us suppose that there were a land like Narnia and that the Son of God, as He became a Man in our world, became a Lion there, and then imagine what would happen.1
Aslan's How is the setting of one of the most powerful and allegorical scenes in the book. When the White Witch means to exercise her right to kill Edmund (a betrayer), Aslan offers his own life instead. The White Witch delights in this and thinks that she has won for she has killed Aslan and can now rule Narnia unopposed. The two girls, Susan and Lucy, witness the Stone Table cracking and Aslan, paralleling Jesus, returning to life. Aslan then goes on to defeat the White Witch and heal the animals that had been turned to stone.
Aslan's How is seen in both The Lion, The Witch and The Wardrobe and Prince Caspian, but by Caspian's time, it has been covered and is now underground. Caspian is advised to set his camp there because it offers the best position to combat his uncle, Miraz, and it is home to the deepest magic Narnia has ever known.
1 - C.S. Lewis: Letters to children, pp 44-45
reading The Lion, The Witch and The Wardrobe and Prince Caspian