Cerberus' fountain or the Dragon fountain awaits us.
Its purpose is to warn he who has dared to pass through the egg.
He can take these marvelous flights of stairs, which will lead him to the various levels, which will bring him to the demigods and, a little farther on, to the gods.
He has to have passed through the egg, to have been reborn. He has to have triumphed over Cerberus' fury to contemplate the gods, face to face.