Begin your page with the words, “Well, you could make a fort out of…” Then finish off the sentence with whatever pops into your mind next. Let the word well give you the freedom to say any old thing. It signals that you haven’t committed to coming up with a good idea, just an idea. See where that idea takes you.
It might turn out that you write a page that looks like a list of all the different things a fort could be made out of. Or it could be a detailed description on a single fort that you can see in your imagination. Or a combination of the two.
However it comes out, when you get to the end of the page, look the whole thing over. Add or change a few words. Include a bit of illustration if you haven’t already.
Give your work a title. Sign the page and date it, too.