For the adventures Mandy and Kier. There would probably be some sort of rope swing connectors between Mandy and Matts house, maybe all over the place, but totally undetectable unless you new about them.
The TreeHouse Workshop is a Seattle-based company that takes the art of constructing tree houses extremely seriously. They build an average of one tree house per month and hire extremely able builders and carpenters to construct their projects. Their finished works vary in luxury but some even include (counterintuitive!) fireplaces.
Cedar Spire (Fife, Scotland) A fairy-tale castle sits on the grounds of a grand Scottish estate. Its majestic details include: stained-glass windows, conical roofs and a balcony that's perfect for playing Rapunzel.