I thought that maybe I'd occasionally rent a car and drive out to a state park, but what I quickly discovered was that, once driving stopped being a part of my daily life, the idea of regularly driving out to a forest preserve lost its palatability. Largely because I am no longer inured to driving, so any plan for how to spend my leisure time that involves devoting a significant percentage of it to being stuck behind the wheel on a freeway is kind of a non-starter. So instead I road bike 4 seasons and take a few camping trips per year. So far it's working for me. Less time stuck in a car and more time out walking in my neighborhood means I have a greatly reduced need for things like mountain biking to help me unwind in the first place.
That said, I think that when I originally calculated it out, I figured out that renting a car 4-5 days a month was still cheaper than owning an inexpensive car. And not too much of a hassle in most cities - out of 4 urban addresses I've lived at, only one wasn't close to a car rental office, and even then it was only about 15 minutes by bus.