The view from the penthouse:

 The penthouse suite, also known as the "third floor" bedroom for the boy!

 There really is this much space: the total size is 5 feet by 12 feet.

 There is plenty of play space at the far end.....

...and we discovered that we can still use the batman curtains from the old bed for this one...still need to be finished, but what a score!  The bat-cave becomes the bat-loft!

I still have a to-do list, and I'm not sure I'll ever be "done" done with this project.  I built without plans and tweaked as I went, so I think I will still tweak along the way for a while.

To do for now:

1. Install rail on wall side. I wasn't going to do this, as it isn't necessary for safety, but it will make it so that you can't fall into the window blinds.
2. Window blinds: Yeah, these are cheap, and we've never replaced them since we moved in. Need to explore options.
3. More reinforcements underneath: I went with 11/32 thickness of plywood. That wasn't a mistake per se as it made it easier for me to wrangle the pieces home and up two flights of stairs (I'm too stubborn to wait for help, I admit it!).  Thicker plywood would be useful, but instead I'm just adding a few more supports underneath with 2x4's.  And 2x4's are a lot cheaper than thick plywood!
4. Hem and hang batman curtains.
5. Take down old curtain hardware.
6. Patch and paint holes.
7. Install some type of lighting underneath the bed for after sunset play.

I think that's it, until I decide to upgrade or change something else! 

Still to come: The space under the loft, and final thoughts, costs and design ideas.  There are always things I learn in these projects that I would do different next time!