Not sure

what this is meant to be, it has recently appeared in the Sandringham arboretum, there's a platform at about head height and the beginning of some wooden steps. It's clearly under construction and the rusty bent pieces of corrugated metal roof lend it an antiquated look. The edges of the roof look sharp and not too safe if youngsters are meant to ultimately play in it.

I'll have a another look in a few weeks.