I recently made the boys a "loft/fort" out of old flannel sheets that is familiar to this. I used cotton twine to hang the sheets on (instead of the poles in this pic) and used ceiling hooks to secure line. I also hung sheets on the bottom bunk too. Can't leave out the bottom bunk! :) We are working on getting some lights and more shelving. They LOVE it.
Well... if I ever get a teaching job, it is getting a bit too late for the Arctic theme, and the Fairytale theme also takes a bit of time to throw together... How about a camping theme? Can change with the seasons! :)