GeoGuessr is a pretty fun online game where it shows you a random location from Google Street View and then you zoom in and click on a world map to guess where you are with points being assigned based on how close you are to the actual location.
There are no “rules” per se but you can either make your best guess depending on where you “beam down to” or you can “cheat” a bit and move around using the keyboard to look for clues – street signs, buildings that have the names of their city on them, identifiable landmarks, etc.
(via MetaFilter who are suspicious this site may be a viral marketing attempt by the Australian Tourism Council since that country shows up a lot!)