The fort depicted here really did exist. It wasn’t as complete as shown in this comic, though. The real one was just a level platform with a plank ladder leading up one of the support trees. It was a short 15 minute walk from my cul-de-sac into the thick of the woods, down an unofficial "well-tread" path. I still to this day don’t know who built it or how old it was at the time I found it.
Unfortunately, time was not kind to it; much like the stepping stones and the oversized piping, this is yet another landmark of my childhood that has not survived. On one of my last trips out into the woods while visiting the old house, I found that the fort had all but disintegrated, either decomposed by the elements or removed by someone. All that’s left of it is a single plank of wood nailed to a tree.