im assuming they should be decently populous / not obscure?
No limitations, since there is nothing to gain by stumping everyone. The "mob rule" provision should deal with anyone who is just wasting people's time.
Well, I thought those blue and yellow colors on the lamp posts and the bus looked familiar, and my friend recently visited Peru and he always asks me to help him pick out which photos to use for his Facebook album, so I went with Lima thinking that I'd seen it in his pictures.
(and the reason I guessed Brussels originally was because I'd been there, so thought maybe it was back then I'd seen it)