Anyway, after finding an Ingress guild on HabitRPG and asking a few questions (mostly, "Are there any players aged 50+ or will I be completely out of place?"), I have downloaded the app and immediately had to go and try it out. I seem to have claimed my first portal! And then I tried to hack an enemy portal and got zapped! At which point my fingers were freezing holding the phone so I walked back home. Anyway, I have downloaded the PDF of the Agent Field Guide, so I have a bit of reading to do. I joined the resistance, by the way, for the completely shallow reason that the Welsh resistance badge looked cooler and someone had bothered to translate the name into Welsh. :)
But as an aid to getting up off the computer and out into the real world to walk about and get some exercise, Ingress looks like a winner. I've already walked an extra miles today on account of the game and I've spotted some portals a little further afield to explore at the weekend.