I use a harness to which I attach one of those retractable dog walking thingies - but I only have 1. So they can only go out one at a time. The other will sit inside peering sadly out the windows at us.
I'm taking them up the driveway, and around the house. Hopefully getting them used to home and where the escape routes are if they ever need one!
You'll never get fit walking a cat. They have to stop and sniff everything. EVERYTHING. EVERY DAMNED SQUARE INCH OF EVERYTHING.
See how I share this joy with you:
Ken couldn't be bothered. He put Snorfs on the string and tied him to a post then went off to do some weeding. Snorfs entertained himself for about an hour.
All went well until Snorfy got himself tangled around a pot plant
We came inside after that and little kittens had a big sleep
The Snorfmeister was particularly tired out