Hiking is a good one, or just spending time in nature in general. I try to do it a little every day. One of the most powerful such experiences I had was walking home from work one day for 45 minutes in intense rain and cold winds, wearing nothing but a T-shirt and shorts, because the weather was nice enough in the morning. It felt terrible for 5 minutes, then I just sort of accepted my predicament and surrendered, followed by a hefty adrenaline rush, and walked home calmly with a big grin on my face, absolutely drenched. Onlookers must've thought I was completely off my rocker, which to be fair is at least partially true...

It can be very freeing to just surrender to nature some times.

Though I don't necessarily recommend trying this at home, especially if you're immuno-compromised.