I heard this on the radio the other day, on some eclectic program, as I don't listen to any show or station which would play this sort of thing on a regular basis, if in fact such things exist.
Anyway, I hadn't heard it for probably 40 years, and I had to go to youtube and reacquaint myself. An interesting nudge in the brain cells; such a simple tune but so rich in possibility. Turns out there are about 10 live versions on youtube, and the improvisation is completely different, both in form and feel, on each of them, but this one seems a good representative. Apparently truncated from 17 minutes, but there doesn't seem to be a whole one posted, and that is probably too much for most people's attention anyway. (The video imagery is a bit inept and heavyhanded, although it gets better after a while, but not really recommended, best just follow the audio):
