After receiving the clue from Old Kasuto, you'll need to carefully interpret it to find New Kasuto. New Kasuto is often located in a very obscure spot, sometimes requiring you to walk through a specific tile on the overworld that appears to be a dead end, or to use an item like the Cross to reveal a hidden path. It's usually in a remote area, far from other towns or palaces. Once you find the entrance to New Kasuto, you'll discover a bustling town. Explore all the houses and speak to the villagers. One specific wise man or elder in New Kasuto will bestow upon you the Magic Key. This item is a permanent addition to your inventory and will automatically open any locked door in any palace or dungeon, eliminating the need to search for small keys. This is arguably the most valuable side quest reward in the entire game, making dungeon exploration significantly smoother.
