I liked this as well.
The main problem I had when I started was I hadn't read your instructions properly and couldn't work out why the tourist wouldn't move anywhere (I forgot about the initial compass direction). Once I started again (and paid attention) it flowed smoothly between tourists and I didn't get any errors. It could be helpful if it's possible to log that a user isn't inputting commands properly and give them some feedback (it doesn't have to be polite!).
Were you thinking of adding any modifiers in that would change how you might have to give directions - a sort of puzzle mechanic? (something like traffic that could move at the same rate as the tourist and block certain intersections)
I'll be interested in having another go when you get further on. Great job with what you've got so far.