After you obtain the Owl Bomb in Baldo The Guardian Owls, use the bomb to blow up a wooden crate in front of the bakery in Rodia Town. Head through the small opening to arrive in The Bakery Pantry dungeon!
Defeat all the rats in this room then proceed through the door up the stairs. Again, defeat the rats in this room and push the wooden box towards the ladder to plug the hole they’re coming through.
Head on up the stairs. Throw a bomb at the large wooden crate to continue on.
In the next room, push the wooden crate trapped by a spider web to the northern side of the room to block the hole the rats are coming out of.
Head all the way back to the starting room. Defeat the rats in here again then use your bomb next to the torch on the wall.
The cracked wall will crumble, revealing a doorway. Head on through. Move the wooden crate in the northeastern side of this room to block the rats coming through then blow up the wall on the western side to reveal a path. Proceed forward and take out all the rats. Use the pots for the ones you can’t reach. Unlock the door at the end of the path and go through it. Push the boxes as shown below to create a path.
Afterwards, head down the stairs and stand on the pressure point to lower the gate blocking the door.
Push the last box into place and continue through the door. Defeat the rat boss. When he gets close, dodge past him when he swings at you then strike his back. He’ll raise up on a rope and hang from the ceiling. Little rats will spawn and the water will raise. Head to the northern corner and throw a bomb at the mechanism to lower the water, which will make it easier to dodge. After he’s been defeated, the cage trapping the cat will raise. Exit this room and head up the stairs. On the northern side, walk up the plank then enter the door.
Speak with the cat to find out that it’s Camuria! He’ll tell you to meet him at Maneko’s house so head on over there! When you speak with him there, he’ll give you the Cat Door Key. Next, head to Naneko Town and speak with Amu, the Cat King. He’ll tell you that the medallion will open a door to where the Key to the Furnace is held. The Owl Furnace is located to the highest, northernmost part of Leone Heights. Head to the northwestern part of town and use the key to unlock the door. Head inside to obtain The Great Owl Furnace Key. This will trigger the quest called The Owl Furnace.