I generally do not encourage people to exercise, at least not like I once did. Exercise I think is one of those things where discussion never is anything like the real thing. This discourages a lot of people.
I would generally recommend something like social soccer, since there is a more balanced support structure imho. I used to easily run a 20 km jog on a Saturday, but this serves no purpose to mention other than to seem competitive.
For me, exercise is not an easy fix. It is one thing of many, which can greatly enrich one's life. Something like being into music can be on par with exercising, especially if one is unlikely to be able to exercise, whether because of mood or physical barriers.
But having some sort of encouragement, whether exercise, music or intellectual or otherwise engaging pursuits is key to me to become a happier person. Dark days in and of themselves are not necessarily a burden. In some way I would paraphrase this: "more life, not more effort". Being more relaxed towards life has been a strong motivator for me.