vienna  aha:!!

it's the middle ages, you're travelling across europe and you want to find the way to vienna. you come to a crossroads, now there are two ways to go. at the crossroads stand a knight and a knave. the knight answers every question truthfully. the knave answers every question falsely. you don't know which guy is which. how can you figure out which road leads to Vienna by only asking one question?

thanks dr. james and reuven