I have gotten into the habit of going out for a morning powerwalk right after I wake up every day. Because I go out so early, I get to watch the sunrise every day and it has a great effect on my mood. I stay outside for maybe 1-2 hours (depending on how far I walk) before coming back home, having a big glass of water, jumping in the shower (I did cold showers during the summer, but now it's getting so damn cold that I have started taking hot showers again for now - otherwise I'd sit and shiver all day) and then have my morning coffee.
I have been sick for the last few days so I took some time off from this routine to rest and even though it was only for 3 days, I immediately felt very different. The muscles in my body became stiff, my mood got worse and I started having trouble going to sleep at night.
I woke up this morning and immediately headed outside for the first time since my days off and I already feel so much better. I admit that getting (back) into the habit can be difficult (I spent about 10 minutes sitting in bed grunting and moaning about having to go outside this morning) but the reward is worth it, 100%.