Two domed caps of different heights, clad in cedar shingles cut in a fish-scale pattern and stained three shades of gray-brown so the color shifts slightly as the shingles weather unevenly, the way real fungus does. The smaller cap holds a loft just tall enough for a six-year-old to stand in; the larger one is the main room, with a round window cut low enough to see out of while sitting on the floor.
The exterior walls below the roofline are finished in chalkboard paint on three sides, which turned out to matter more than the architecture — the client's daughter repaints the whole thing every weekend. A Dutch door lets a parent lean on the bottom half and talk without ducking through a full-size opening built for someone half their height.
Nothing structural above four feet: no ladders, no drop-offs, nothing requiring supervision beyond what any yard needs. It's meant to disappear into unsupervised play for hours at a time.