Preparation is key!
Ask yourself:
What are your learning goals?
What physical things do participants need to do to show they have met the learning goals?
Write out the physical things students need to do to show they have mastered the learning goals, then pair those with clues and puzzles.
Example
Learning Goal: Students know they can find information about the library on the library website.
Physical Act: Students use the library website to look up library policies.
Clue/Puzzle: Students find a set of questions about library policies, and a sheet of paper with four sets of fill-in-the-blank. Only the right answers will fit in the spots. In each answer there is a square around a particular letter. When the four correct letters are found they are the combination to a lock.