Catios: The Safe Enclosure for Cats

Many cat owners have come to the conclusion that their cats need to be 100% indoor cats for their own safety. I totally agree that this is safer, because the risk of my cats getting eaten by some animal, hit by a car, or any other potential danger is reason enough to keep the doors shut. However, cats were made for the outdoors! They deserve to nap in the sunshine, chase bugs and feel the wind lift their fur. Keeping them from that is cruel in its own way, I think. So what is the solution?