Explore the local area. Answers to questions create a grid reference - what is there?
Beforehand, go to at least 6/8 places in the area and make up a suitable question that has a numerical answer. i.e. last number of the phone number on the window of Pappa Johns.
With your 6+ numbers, make them into a grid reference in your area. Then identify what is there - that's the final answer.
Numbers could include:
* Phone number
* Last delivery time on a postbox
* Lamp-post identification number (lampposts often have numbers on stickers)
* House numbers
* Opening hours
* Price of something on a menu
Give the teams a map, list of grid references questions (in a random order).
They should plan their route and go and find the answers.
They should the assemble the resulting grid reference and leg it there (or back to the hut with the answer)