Our club does an annual underwater scavenger hunt. Local dive shops, dive sites and divers donate prizes. Buddy teams are given a list of items they need to find, such as a fin or bouquet of flowers (artificial, of course). These items are placed at the dive site in various places, some easily visible others you have to "search" for. The items have multiple tags (plastic caution tape cut into strips). When the team finds the item, they pull a tag and leave the rest for the next group. In our case, the hunt lasts from 11-1 PM. The divers have to be out of the water and checked in by 1. At check in, the number of tags you've collected are counted. The prizes are laid out on a table and the buddy team with the most items collected gets first pick, then the next and so on until even the team who came in last gets a turn. Then it begins again. Usually we have enough stuff donated that each team gets at least two chances to pick something. A new diver has just as much fun as a seasoned diver. The divers who place the items usually work as safety divers or will accompany a new diver buddy team. We have a bbq or potluck lunch and everyone shares their stories of the day.
Hope this helps. It's something we all look forward to doing. Oh, and if you are a member of the dive club you have free admission if not you have to pay a minimal activity fee. This helps promote membership and recruit new members.