The treehouse was commissioned by a friend; he wanted the top floor to be an observatory, so I had to make the house tall enough to clear the crown of the tree. I created it in Blender.
The tree is an XFrog freebie, an english oak. All the trees and shrubs are from XFrog; the grass is from Turbosquid. I created the kayak-- you can find it at
Blendswap.com. The motorboat is originally from Blendswap, but I modified it substantively. Some of the rocks are from Sketchfab.
Attached are a few WIP images of the treehouse showing its structure more clearly. I'm quite proud of the staircase.