Mine would probably be Loch Ness too Liz. I was going to do it as well, as we usually go to Scotland every year and my wife was happy with my plan, but, plans have had to change and we now can't go in September. Gutted.
Another interesting question is, what if you could only do one more race, ever? I think mine would either be Comrades or Marathon des Sables. Not next year though, I'd like a bit more time to prepare!