To step it up a notch, I put on a weighted backpack (i.e. ruck). I'm typically carrying 30 lbs, sometimes 50. This raises the heart rate and roughly doubles the caloric burn. Low injury risk, too. Michael Easter's book "Comfort Crisis" has a nice chapter on rucking.
I just wish it was easier to contact nature on my walks. I live in a big urban centre, so it's not always easy. But at least urban centers can facilitate social walking -- I've found some fantastic Meetup groups where I can partake in social hikes.
Can't say enough good things about walking/hiking/rucking. It's foundational to the human experience. Get outside, everyone :)