Sitting outside in moonlight on purpose, usually for twenty minutes or so, usually near the full moon. That is the whole practice.

Ayurveda has a version of it, chandra snana, prescribed as cooling for conditions read as excess heat, and modern wellness has picked the idea up more or less unchanged. Moonlight is four hundred thousand times fainter than sunlight, so nothing measurable is being delivered. Being outside at night looking up is doing the work, and that is not nothing.