Here's how you can get to it:
1. Enter the castle: The entrance to the castle is located near the top of the hill.
2. Find the knight's statue: The statue is in the main hall of the castle. It will be visible once you enter.
3. Interact with the statue: Interact with the statue to reveal a hidden trapdoor.
4. Go through the trapdoor: This will lead you down into a hidden passageway.
5. Follow the passageway: The passageway will eventually lead you to the well.
Important Note: You'll need to solve a few puzzles and overcome some obstacles before reaching the well, as it's a key location in the game's story.