Not that I don't have enough on my to-do list... but I recently threw a sand box right at the very top. Like, you have to stand on your tippy toes to reach that high...
This is my inspiration.
click over to see how it converts!
But I drew up a modified version for myself.
(the second one doesn't have the last two boards drawn-up because... I didn't capture the screen when I had it up)
If my version works, I'll take a few minutes to draw up the full plans for everyone else, because not everyone wants a 2 x 2 foot sand box :-)