What I expect is an animal containment door, there is a caution may bite warning so I don’t know what else it could be. It must not have washed up here to long ago perhaps from here, though it doesn’t look like something from cobalt, perhaps another island then, maybe its just as crazy as this one, huh unlikely. Anyway this door is definitely a Big One, thick and strong and I wouldn’t be a Clever Girl if I didn’t decide to use this as my front door. No one’s going to Shoot Her up in a hurry. ;)