The answer to all your questions is "I have no idea"!
I don't know who. I don't know why. I don't know how. I don't know why there. I don't know the purpose. But it sure is interesting!! The only thing I know is that, according to the sign, it was built in 2013. I don't know how many hours went into it, but I'm guessing lots! Share your thoughts in your log after your visit!
There isn't much to say other than someone obviously spent a LOT of time building this structure. It looks fantastic and is very well constructed. It really has to be seen in person to be believed! I'm not sure the structure will survive, so I decided to hide the cache on the nearby hilltop rather than in/near the cabin.
Reaching the cabin is challenging. You can link together a traverse from the summit of Anklebiter Ridge, though some routefinding is required. A gully north of Anklebiter provides access around some tricky terrain, though it will likely accumulate and hold snow for most seasons. Once back along the ridge below Anklebiter it is more or less a ridgewalk to Bluemat Hill with a few small difficulties. Descent can follow to the south - I found a nice scree descent followed by steep bushwhacking to reach Hwy 1A. It's not easy, but hey, at least you're not lugging up the materials to build a giant cabin in the middle of nowhere!
Looking out from inside the cabin: