Litter box in garage such a good idea! One commenter noted a potential problem with the car exhaust in the garage and the cat door--whether it would be sufficient to keep it out. But we had a cat door in our old house to the garage and never had an issue.
Minimalist IKEA Cabinet Hack, and lots of other ideas on hiding a litter box. Not just for the litter box but for a dog's or cat's pet bed, when company is over or just during the day, just shut the door and it won't have to be seen until bedtime.
The Best Hammocks for the Most Relaxing Summer Ever