Is the playhouse evil or magical, or was it just the narrator's imagination?

The playhouse appears to be magical, as the door opens and closes on its own, and the older boys disappear inside it. It seems to be evil because of the horrible door knocker that frightens the narrator, and the fact that it seems to have swallowed the boys. However, it is possible that the boys were hiding in there, or that the narrator was imagining the whole thing. It seems more likely that the boys disappeared inside the playhouse because it is where horrible things happened in the past. The old man explains that his father made the playhouse for his own games, suggesting something very sinister. The old man also mentions being locked in cages by his father, suggesting that he was abusive to them. The playhouse may not be intrinsically evil, but it has taken on an evil atmosphere by association.