A bed loft that doesn't touch the wall on all four sides: Separation wall (with space at the top), maybe it could be covered with apple crate pieces? Or just re-purposing any kind of cool wood. And don't look at the window bit.
I really wonder if this dog has to share his/her nook with a bunch of puppies or kids romping all around playing hide and seek. Oh, and note the shelves that are lined with doormat material! So smart and tough.