Go for walks where the walk is the point. Walking with a destination in mind is totally fine too but the best is a walk done just for the sake of walking around. An amble, a stroll.
In the summer, when there's still plenty of daylight once dinner is done, my kids love to go for a walk around the block. They conduct little races, find sticks to fence with, collect leaves, notice birds. My wife and I stroll behind them, probably at half the pace we would otherwise walk, enjoying the fresh air and the obvious pleasure the kids take in the activity.
Kids can learn to love walks very quickly. Notice I'm not saying "kids love walks"... because the reality is, over a certain age, walking for walking's sake is a bit of an acquired taste. But once you get past the initial resistance, walks are great. There's lots to notice: people to see, different cars or buses or plants or animals, interesting houses or surprising things on balconies. Start them young enough, and all of this is an easy sell.
I've always liked going for walks, but I had to kind of trick my eldest daughter into enjoying walking. Here's how I did it: I told her we would walk to the corner store for freezies. That was enough of a motivation, but it wasn't a real destination. It was clear that going for the walk was the point and freezies are excellent treats to walk with.
Now I know that I'll get a moderate to significant amount of resistance when I propose a walk but that as soon as we are out the door, my daughter will enjoy every minute of it.
"Going for a walk" is an excellent activity for when you don't really know what else to do. It comes by default with a whole set of features that you probably want in an activity: it helps get some energy out, it doesn't involve screens, it's good for you too, it can be done well in 10 minutes or stretched to 30 (or 50, or longer!). As far as "kid activities to have in your back pocket" go, going for a walk has to be one of the best.
One of the things I like most about walking is that it helps you establish yourself (and your kids) in the world immediately around you. It's hard to go for a walk and not get a little more connected to your neighbourhood, your local environment, the people and places close by. Driving somewhere and then walking is totally fine too... but it isn't really what I'm talking about here.
So go for an amble with your kids. If you all need a bit of motivation, give yourselves a destination and a reward. But hopefully you'll all quickly enjoy the walk itself, for itself.