Free self-guided itinerary. This is a travel guide, not a bookable guided tour.
Most one-day plans for Tallinn spend the whole day inside the walls. The old town is small and can be walked properly in three or four hours, after which most people are looking at the same streets again.
Morning. The old town, early, before the day visitors arrive. Upper town first, lower town after.
Lunch. Outside the walls, where it is both better and cheaper.
Afternoon. Kalamaja and the former industrial quarter, or the shoreline. This is the part that makes the day feel like a city rather than a set.
Arriving in the old town at midday on a cruise day. Eating on the main square. And assuming the wooden districts are far away — they are a fifteen-minute walk.
You will not need transport for this plan. If you do, the trams are simple and the city is small.