In Second Life, a sandbox is any area set aside for communal creation. You can enter any sandbox at NCI and create basically anything your imagination can come up with. NCI Kuula has a sandbox. NCI South has a sandbox. NCI Beach has a sandbox. And NCI Wiki has a sandbox also. Unlike most of this wiki, the sandbox is open for everyone to create and edit. That's right, everyone.
As NCI is a community centered around Second Life, it would probably be a good idea to write about either NCI or Second Life. Have a guide you've been itching to share with the world? Or a travelogue of amazing places you've visited? Write about it! Even topics like general computing are fair game. Here's the big thing: if you make a page that's really cool, or is really useful, or both, we'll find a place for it in the main part of our wiki, enshrined with your name on it. This is your community and your wiki, we're just running it.
Of course this all comes with some responsibility, so there have to be some rules. They're pretty easy though, nothing really earth shattering. They're pretty much exactly the same as our inworld sandboxes.
One other thing to keep in mind is that this wiki, like most public wikis (including Wikipedia) will identify article authors and editors by IP address. If you would prefer not sharing that information, NCI features several similar creative outlets. Perhaps turn your proposed wiki page into a forum topic!