As you explore the Clock Tower, you'll eventually find a room with a large body of water. You'll need the Undine Soul (Ability) to cross it. This soul is dropped by the Undine enemy, which can be found in this very water. Defeat an Undine to acquire its soul, which allows you to walk on water. Once you have it, you can cross the water to access new areas and continue your progression. This soul is also vital for reaching hidden areas in other parts of the castle.
