A photo scavenger hunt is one of the easiest sidequests to run because the proof is built into the activity. Friends do not need to explain what happened; the photo does the work.
Simple photo hunt prompts
Ask for a red sign, a weird menu item, the best poster, the oldest-looking doorway, a reflection photo, a group shadow, or a picture of something that looks like it belongs in a movie.
Make it work anywhere
For parks, use trees, benches, paths, and sky. For cities, use windows, signs, receipts, and transit stops. For house parties, use snacks, playlists, outfits, and tiny details in the room.