I agree to all what has been written. From my experience the most interesting places to go (at least for my taste) assuming that you just want to stay in a interesting bigger city, look around etc witout spending too much time, good food etc). So no countryside, no places hard to get to (like Lake Titikaka). The list is incomplete but should give you some ideas

Europe: London, Rome, Barcelona, then Berlin, Prague, Vienna, Budapest

US: New York, SFO

Southam: Buenos Aires, Santiago

Asia: Hong Kong, Bangkok, then Tokyo

Australia: Sydney