My wife got the Rapunzel's Tower of creativity set a while back, but was kinda disappointed that it was completely open on the back. I therefore decided to buy another Tower of Creativity set (and thereby acquire my own Rapunzel, Flynn & Pascal figures) and see if I could do something about that.
Here's the result:
Rapunzel's Tower Front by Hikaro Takayama, on Flickr
As you can see here, there isn't too much noticeably changed on the front, however if you turn it to the side:
Rapunzel's Tower Side by Hikaro Takayama, on Flickr
...You can see it is now fully enclosed. It splits apart on the seam and is held together with 8 technic pins at strategic locations.
I also decided to make it so that the back wasn't an exact duplicate of the front for a bit of variety:
Rapunzel's Tower Back by Hikaro Takayama, on Flickr
My wife, needless to say, was quite pleased with the results. The only thing I'd like to work a bit more on sometime is the interior... The back side is relatively bare at the moment.