The quest "Sealed Away" in the player's notebook says as follows: Once the player tries to move the rock alone, the notebook will update. As soon as the player gets help from a salt-water dolphin partner to move the rock aside, your notebook will wrap up the notebook entry. Completing this quest is the only way to unlock the Pygmy Sperm Whale that was trapped inside of the Cavern before the player moved the rubble blocking the entrance aside.