The White Crystal is a key item that allows you to reveal hidden platforms and passages. If you haven't purchased it yet, you can buy it in Ondol for 50 Hearts (or in Jova if you missed it earlier).
- Locate the Hidden Path: From Ondol, head right. You will come to a dead end with a cliff face.
- Equip and Use the White Crystal: Stand at the edge of the cliff. Open your inventory (Start button), select the White Crystal, and then press the B button to use it.
- Reveal the Bridge: The White Crystal will cause a hidden bridge to appear, spanning the gap. This bridge is temporary, so cross it quickly.
This hidden bridge leads to the next mansion, the Bodley Mansion. Be prepared for a challenging area once you cross.