really simple.
you have a start point...the route is unknown until you are given directions(cryptic that is) on the day.
each person is set off at x minutes intervals.
you have clues to find, could be phone numbers in telephone boxes, numbers on Doors...whatever, could be anything.
its all judged on a point scale....from the clues you found, the time it took you, and the distance travelled.
the finish point can be anywhere, but best to be where you started from, just incase anyone screws up completely and they can return to base .
i have been told it is good to do the route doubling back on itself (but it may not be)....that way you meet others coming the other way.......lol