My basement is fairly large. It runs the entire length of the house, but doesn't have any dividing walls. Like most basements, it's used as my catch-all storage. That being said, it's probably not a good idea to let kids have free reign down there. I couldn't put up actual walls, because as I said in my first post, I didn't want anything permanent or even semi-permanent, and I didn't want to spend a lot of money.
Also, I didn't want to box these kids in, I just wanted to define their space a little. So, how do I provide a barrier, make it fun and keep it cheap? PLAYHOUSES! Those are definitely fun. There's no point exploring the rest of the room is they have their own little world to play in. But, cheap? Hmmmm