Giaguara describes, and I agree: Cat room. This would be awesome. To be then connected to a catio, and a small snuggly corner with bookshelves where the humans and cats could have some proper snuggly time.
My cat loves our bird feeded in the window! This is a great bird feeder because it sticks to the window (so the children and cats can see the birds up close), and it has a one-way mirror so the birds don't see the cat and the kids! Holds plenty of food.