I started with the original plans for the sandbox with the benches, and then just sort of took off with the modifications.
When it's open, it's a 4'x6' sandbox with a bench on one side and a canopy overhead. When it's closed, it's a stage complete with curtains, or can also convert into a puppet theatre.
I had to make several adjustments to the original plan to allow for enough support for the stage to be walked (and danced) on, including an extra armrest in the bench, and a few blocks built up from the base of the sand area. I also used 1x6 boards for the top instead of 1x4, to cover the entire 4' with only the one bench.
Thanks so much for the plans, my girls love it! (and thanks to KnittingEmily for posting the plans for the 6' sandbox, which gave me a jumping off point for the sizing I used.)
The story of how I built it can be found here: