However, a certain amount of activity is required to maintain a minimal amount of fitness. Smart training can even take, in worst case, one hour a week.
What I typically observe in people who refuse to do even the bare minimum of activity, is that they find a "non-activity", and pretend it works.
What they're actually doing is instead to find something that takes virtually no effort while giving the illusion that they've absolved the duty.
Very typical non-activities: walking and climbing stairs.
(This is a bit complex suject of course, because if we take somebody who sits 24/7 on a chair/couch, of course walking is better than nothing - but I'm referring to the principle)
However, this is a bit odd in context. If one considers a population where 60%+ of the population has 30%+ of bodyfat percentage, then it's impossible to define what constitutes fitness - even one flight of stairs, in a sense, requires a decent amount of training.
In at least northern Europe, hiking is relatively common for elderlies (people in their 60s) - and this amounts to hours of walking in rough terrains, so definitely, for a person who's not (considerably) overweight, and hour of walks in the city is... a walk in the park.