There would be a lot more than one! if the world were a different place I'd have loved to have visited great swathes of the Middle East/North Africa, I have only done Israel but all the following appear very interesting to me, Egypt, Algeria, Morocco, Libya even, although my dad was there in the war and told me his enduring memory of it was sand! sand! sand!
Syria, Lebanon, Jordan, Iraq, Iran.
I have luckily done parts of Canada, a lot of the US both East and West coasts, Mexico those are all places I'd go back to. I've been drawn to South America ever since my class did it in first year at senior school, I always wanted to go there, I have been to Argentina, Uruguay and Brazil but would go back and do the whole continent in a heartbeat, if I were younger.
Apart from visiting Denmark, I'd like to do the rest of Scandinavia but oh soooo expensive 
New Zealand and the rest of Australia, I've only been to Western Australia, Perth in particular.
In the Far East I'd like to go to Japan, I've been to Singapore and Malaysia but Asia per se would be fairly low on my list behind other places and I have no desire to ever go to either China or Russia, for various reasons they don't appeal to me.
My problem now is, I positively hate flying in spite of having done my fair share and the whole palaver surrounding airport travel gives more anxiety now than it used to. I'd never say never, but I think my days of very big holidays are behind me.