EDIT 14/2/19: I accidentally uploaded the wrong treasure hunt, apologies! This has now been fixed.
A Treasure Hunt on ratio questions of the form: Hugh and Kristian share some money in the ratio 3:4. Hugh gets £18. How much does Kristian get?
Stick the questions up on the wall around the room. Students pick a starting point, answer the question, and look for their answer on the top of a card which tells them where to go next. They end up back at the starting point if they complete all 20 questions correctly.