Empty Space in the backyard...what to fill it with?

So in our backyard we have a basketball hoop on the driveway, little gardens all around, an old wooden treehouse, a large patio and rocks surrounding it, a birdbath, and a lot of trees. We have a pretty big backyard and it's filled all around except for one spot now. There used to be a round trampoline there but now that trampolines are basically illegal (we live in NJ and the insurance company now refuses to pay for trampoline injuries because theres so many...they don't wanna pay even though thats what they're for, but aside from governmental issues...lol) we had to take it down and now theres a big empty spot. No plants can grow there because next to our house is an apartment building that blocks out the sun in that area and too many trees surrounding it. We don't know what to put back there. We have a swing but thats on the patio. Anyone have any ideas?