Way back in 2007 a group of random folks came together and built the Steam Punk Tree House in Oakland. Those folks remained friends and later evolved into what is now the collaborative group, 5 Ton Crane, makers of other, similar projects such at the Ray Gun Gothic Rocket, The Nautilus and the Sub-Sonarium.
The tree House now lives at the Dogfish Head Brewery in Delaware, where it is occasionally featured in their marketing bits.
Here is the latest, and in my opinion, the best one so far.
Note the curly metal work on the front door handle and the interior railing. That was me.