We scouted the back yard for a good location. After deciding that I didn't want to attempt the kind of tree fort that is built around a single tree, we selected four trees in a roughly rhomboid distribution. I took measurements, drew up plans, ran kite string where the beams would go so that I could get things level and squared off, and then measured again. We bought lumber and other supplies.
It was planned to be a platform of approximately 12 feet by 6 feet, 7 feet off of the ground on the low side and 16 feet off of the ground on the hide side, due to the slope of the hill.
I framed the perimeter and then began squaring off the interior:
(As you can see, I had some difficulties pounding the nails all the way in, even using a sledge hammer; thankfully, they were only one of three redundant means used to attach the beams to the trees.)
Finished squaring off the interior:
I decided that the lives of my children were worth the extra $20 and two hours of digging, so I put in two support columns:
I wrapped all of the corners with thick nylon rope, also running it between and threading it through a 4 foot "garden wall":
Added the platform:
Nailed the platform in a little more:
Another view of the underside:
Max cautiously tests it out:
Ran a rope along the top, flipping the "garden fence" up where it belonged. Max, Nathan, and Molly try it out.
Since those pictures, I ran out and got some more braces, then added another support beam beneath in the rain this evening. I'm pretty sure I'm done now.