Christopher Patterson and Lance Barrie on the ideal city:

The idea of the 15-minute city, according to its originator Carlos Moreno, is that people are no more than a 15-minute walk or bike ride away from all the services they need to live, learn and thrive.

For mental health and happiness. I think Geneva more or less meets this criteria. Reykjavík less so, but the potential is definitely there and this kind of approach could be a driving force when developing the city for the future.