Catios are permanent outdoor structures (made of wood and wire, among other materials specific to the design) that give your cat the outdoor experience without all of the risks. Potential alternatives to catios for use both indoors and outdoors exist, but they come with a great number of disadvantages.
Portable enclosures may seem advantageous but are less stable and more easily escaped. There’s also a greater risk of other animals getting into the enclosure. Weather can also be an issue; storms and wind may easily damage a non-permanent structure, regardless of whether your cat is inside.
This takes dedicated walking time and decent weather. There’s always the risk of your cat slipping the leash or encountering aggressive off-leash dogs. Some cats refuse to walk on a lead entirely, making accessories a waste of money. Catios offer "lighter supervision" and are better for busy schedules.
Backyard fencing often has too many holes to escape from, and some cats can scale fences easily—especially chain link. Just as easily, other animals can enter the space and attack pet cats in their own yard. This is not a secure alternative.
While great for climbing, cats miss the authentic experience of the outdoors—the sights, sounds, and smells just beyond their reach. Additionally, some cats ignore custom walkways entirely, preferring the tops of your cabinets and knickknack shelves instead.