Very tough. I got three - Longyearbyen, Nadi and Akureyri - but only because I have visited them. I recommend all three for tourists, but for very different reasons.
Being very tough is the point of the quiz. Also, I had only heard of Longyearbyen, Alesd, and maybe Tamarin before making this. Just zoomed in on a map until I found a city which when I searched it, no other results came up except for in that same country. Haven't even been out of my own state.