An Antique music box. I tried to make a video of the creation of the music box and final image but lost a bunch of the slides. Out of frustration, this one didn't get finished until I had nearly forgot about it all.
This image rendered for three days on 4 computers before crashing, and losing all the work. I rendered again at wallpaper sizes only, just to get it online. I may never try rendering a commercial version of this one again.