Max enjoys his “catio” in Seattle. (Photo by Dan Reeder)

What, cynics may ask, distinguishes a “catio” from a “screened-in porch”?

They clearly haven’t seen the catwalks that wind around Dan Reeder’s Seattle house and yard like a supersized Habitrail with, as he wrote on his blog, “everything a cat could want in that place, including a catnip plant.” It features night lights for nocturnal prowls by his feline, Max, as well as a heated bed.

Dan Reeder’s catio lights up at night. (Photo by Dan Reeder.)

Or consider the complex structure, with bridges and mazes with 20 different levels, at the Monroe, Wash., home of Dennis “Cathouse Man” Gallagher. Or the elaborate enclosure in Lehigh Valley, Pa., about which Julia Konya acknowledged in a how-to post on her design blog: “I’m sure a lot of my neighbors thought that I had finally lost it.”

The catio’s moment in the sun — in shelter magazines, on social media feeds and even used on Craigslist — was probably inevitable. As the cats in our homes (35 percent of U.S. homes have them) slowly take over their interiors (pet industry figures say 74 percent of pet felines have scratching posts, while 25 percent have “kitty condos”), it’s logical they would encroach on exterior spaces, too.

But for owners long shamed by vets and public service announcements urging that felines be kept inside, catios are a safe option for those desperately pining for the outdoors. And for bird lovers — cats’ greatest critics — they’re an appealing way to protect nature’s feathered creatures. In several U.S. cities, bird and cat organizations are teaming up to promote the enclosures on guided “catio tours.” Out West, the Feral Cat Coalition of Oregon and the Portland Audubon Society will join forces on Sept. 10 for a fourth year.

A multi-leveled structure from Dennis “Cathouse Man” Gallagher’s catio in Monroe, Wash. (Photo courtesy of Sharon Ronsse)

But catios are also fantasy structures, like doll houses or dioramas, where creators can construct — and project — their own idealized worlds.

I felt so bad about them never lying in the sun,” Julia Konya wrote, “breathing the fresh air, watching birds, squirrels and butterflies.”

When it came time to make a catio, Reeder wrote in an email: “My goals were pretty ambitious.” And they continue to be. He recently extended a catwalk into a 200 square-foot space that had been his daughters’ playhouse.

“I know it sounds paranoid, but we live in an earthquake zone here in Seattle, and we wanted a place away from the main house (in case it was damaged) where the cats could go and feel comfortable.”

Too much? “For what it’s worth,” he acknowledged, “the cats would have been very happy with much less.”

Ah, but would we?

Below are some of the most elaborate catios we could find. If you’ve built one of your own, please submit photos using the link at the bottom of the page. We may feature it in a follow-up post.

A small part of Dan Reeder’s elaborate catio. (Photo by Dan Reeder)

In Oregon, this enclosure made the 2015 Portland Catio Tour (Holly Erickson/Audubon Society of Portland.)

This catio also made the annual Portland tour last year. (Holly Erickson/Audubon Society of Portland.)