About 20 yrs ago, our twins and I built a treehouse up in a big old willow tree in the corner of our yard. It was sorta-triangular, and sided with "shiplap" siding, with a 4' carved "tiki" head at the "Prow". Also, at the bottom of the tree is an old aluminum canoe set up as a sandbox. We christened it "Kon-Triki", and it kinda dominates that corner of our yard. A coupla years later, we added a 110' "trolley" line from that to a tree across the yard. The thing has been a tremendous hit over the years. The tree is dying, now, but our kids are grown, with their own little ones, and we're planning bigger and better things in a (younger) cluster of elms across the yard. The "Trolley" is still being used (it is ACTUALLY pretty safe, with no major injuries, yet...) and represents considerable "R&D", the current one being the "Mark 7". Its built from BMX bicycle parts. I'd be only too happy to correspond with people who are into this... Mike