So I was in Traverse Town looking for treasures I missed and I visited the Third District and went to the door with the flame on it. I just now examined it and used fire magic on it. It opened and the little chime that played when ever you do something that's secret played. The door opens and you go into this dark place with a house surrounded by water. You can't go inside it but there's a chest behind it. The house looks really old and abandoned. Does it have to do with Merlin maybe??