Would any of you book a fitness training or detox retreat style holiday? Or have you and would you recommend it or did you dislike it?

I've been wondering about this for a bit and I think this will be the year to give it a try, ideally I'm going to find something or some place that can offer me some sort of three to four week transformation challenge or regime so that I can come back from it with some kind of really tangible change or gain in fitness. That said, I have no idea where to begin looking for such a thing. Just the vague notion that it ought to be out there.