Hiking.
I cannot stress this enough.
One of the biggest loops of depression is feeling anhedonic and drained of energy, which keeps you from doing stuff, which keeps you anhedonic and drained of energy.
Go for a hike literally every single day for a whole month. Rate your depression on a scale of 1-10 every day a week before you start, every single day during, and then every day for a week after. You'll see the trend, and hiking will be your new antidepressant.
It's easy. It's walking. It's not competitive, you can go hilariously slowly and still accomplish your goal. You can add hobbies to this hobby, like photography or bird watching. You're probably not getting enough exercise, and being depressed all the time blows.
If you're nerdy and depressed, you may have heard about EMDR, where you sway your eyes back and forth rhythmically while you think about trauma. The doctor who came up with the treatment (that's showing crazy good results) went down the rabbit hole they went down because they noticed walking in the woods helping their depression. They currently think the mechanism has something to do with bilateral stimulation (walking) and constant reframing of your perspective (tree on my right, tree on my left, rock on my right, rock on my left).
Other physical activities are great too, but hiking seems literally taylor made for the depressed.
Do you struggle with anxiety and destructive ruminative thought patterns? Guess what you won't have the energy to do when you're panting for air?
Hiking is a legit way to maintain depression indefinitely. Don't get cozy, though. take a break and your brain will find its way back to it's old antics.