I'd echo the sentiment about walking; as I do a fair amount of it.
@Iceman can vouch for that via my Strava feed.
Naturally though, unlike a 10k run or 15mile cycle, you've got to put a fair bit of time aside if you want to get out for a decent length walk. Thankfully I have ample time on my hands and get out when I can. I'm certainly no stranger to 8, 10, 15 or even 20mile strolls.
To pop on a playlist or podcast and just wander around is great for the soul. I'll swear by it. Pick a good day too, and you can treat yourself to an ice cream on the route.