I had an appointment with my Cardiologist last week and it turns out he finds my general lifestyle (i.e being two stone overweight, drinking too much and never exercising) far less amusing than I do. And he's sort of told me to sort myself out if I don't want to have a stroke.

Whilst I'm not given to overly-panicking about such things, it would probably do me good to do some exercise. I've got quite a busy and unstructured life though.

So what I want advice on is some form of exercise that

a) Doesn't require me to turn up at the same time at the same place every week

b) isn't really fucking boring

c) in an ideal world will cost far less than gym membership.

Any suggestions?