Thanks for the suggestions, y'all. I can't do this weekend which is a shame as I certainly have demons to slay in Windsor. Bournemouth sounds good (shame about some of the people that live there though!), I reckon I'll sign up to that. Southend is on a day I can't do. Wine estate one is meant to be great although I don't drink so I probably wouldn't make the most of it.
Moar suggestions please!!
I found this one in a "forest" near(ish) me: positivestepspt.co.uk/events/kingsforestmarathon/ 300 runners max, I reckon I could probably deal with that.