From the castle entrance, go north and through the doors, then northwest and through some more doors. Inside, go through the west door, then north through another to find six beds. Examine the clock nearby for an Elixir and open the chest for a Hi-Ether .
Leave and take the door to the east. Rest here if you wish. Leave and go east; examine the pot for a Remedy . Go outside the south door and upstairs. Go northeast and through the door here, then open the chest for an X-Potion .
Leave and go through the south door, then go south and along the path to another door. Go inside and open up the two chests for a Phoenix Down and some Prayer Beads. That’ll be it. Return to the overworld.