I remember reading old client notes from the State Hospitals back when I was working Gero- notes from the 50's-70s (I was reading them in the 90's and early aughts). Some would use the euphemistic term "hydrotherapy," but many used the more colloquial term "packout," as in "patient agitated, 10 minute "packout" with remediation of symptoms". The "procedure" involved disrobing the patient, wrapping them tightly in a bed sheet, and then placing them in a tub of ice water. Miraculously, hypothermia will reduce the intensity of agitated behavior.
In regards to the topic at hand, I think there is a tendency to label a lot of things that just feel good or lead to happiness or a sense of accomplishment as "therapy" or "therapeutic." Having jumped into the cold and icy North Atlantic in January, I can say that the sense of accomplishment of doing something that my primitive brain was telling me very clearly not to do, dealing with the discomfort, and recognizing that my "feelings" about doing something are not always the "facts" about doing said thing felt very nice. It made me happy and proud, at least in the moment. It may have even spurred me to attempt some other "uncomfortable" things in the name of personal growth (though that effect was probably pretty short-term). All those things are good! I'd recommend that anybody- client, friend, stranger on the internet- should seek out such experiences (with all the appropriate medical caveats, of course). Should we call such a thing "therapeutic"? Not unless we can empirically identify the parameters that lead to an practical reduction in the symptoms of a clearly defined mental condition. Do it because it makes you feel good, happy, accomplished, etc., and it is important to feel that way as much as possible. Don't do it to make you less clinically anxious, depressed, characterological, etc. If you do it and don't feel good, happy, accomplished, etc. afterwards, it's not because it "failed." It just didn't do it for you so try something else next time.
TLDR- Not everything that makes you feel legitimately good, accomplished, successful, etc. is "therapy," and not all things that are actual "therapy" will immediately make you feel as good, accomplished, successful, etc. as jumping in the damn ocean in the middle of winter. Do things for what they are, have fun, learn, and grow. While that's probably at least correlated with actual mental illness symptom reduction, it's not a cause of it.