Stretching in the rain
On the practice that grew out of being caught outside one afternoon — and the unexpected things the rain does to a body holding a long stretch.

It started by accident. I was walking the long upper trail above the village when a slow rain began to come in from the west, and I was about an hour from any shelter, so I kept walking. About halfway back I stopped at a small wooden bench I knew well, sat down, and did the calf-and-hamstring set I usually do at that point of the walk. The rain was still falling. The bench was wet. The set took its usual five minutes.
I came home soaked but in a particular kind of good mood that has happened to me a few other times in my life — the kind that comes from a body having been pleasantly used in unusual conditions. The set, done in the rain, had felt different. I started doing it on purpose the next time the weather was right.

What the rain does to the body that the studio does not
Wakes the skin. The small constant impact of rain on the skin, especially the bare arms and the face, sends a steady signal to the nervous system that the body is in contact with the environment. The breath, given that signal, opens up. The shoulders relax in a way they do not relax indoors. The whole practice gets faster.
The cold helps too. A long stretch held in slightly cold air feels different than the same stretch in a warm room. The body has to work a little to stay warm, and the working seems to deepen the stretch rather than fight it. The breath, which would have been ordinary indoors, becomes noticeably long and full. Some part of the autonomic system has been activated by the conditions, and the stretch is doing more for less effort.
On the small practical matters
Bare arms get cold faster than you would expect. A thin merino base layer under a light jacket is the right answer — warm enough not to lose body temperature, light enough not to interfere with movement. Boots with grip, because wet rocks are slippery. A small towel in the rucksack for after.
I do not seek out the rain. I am not, in my middle age, a particularly adventurous person. But when the weather offers it, and I am already outside, the small choice to do the stretching anyway has changed what I think a body is for. The body is not, it turns out, an indoor instrument. It is an outdoor one that has been kept indoors, and the rare days I let it operate in its native conditions are the days the body seems to remember what it was for.