We did a campaign for a marketplace that had users do a scavenger hunt, in which they had to solve a riddle, the answer to which was a product on the marketplace. On that product page, we embedded the next clue which gave them the next riddle, the answer to which was a different product and so on. The prize for the scavenger hunt was free store credit. Initially, we thought that users wouldn’t spend time-solving riddles, but went with it anyway. It turned out that users had so much fun, they spent 30-60 minutes solving the riddles.