Granada's problem is not a shortage of things to do. It's that the city has so many excellent options, stacked in a small area, that most visitors end up at the Alhambra for the morning and then drift through the Albaicín without a clear plan for the afternoon. That approach wastes three-quarters of what the city has to offer.
This list ranks the ten best activities in Granada by the quality of the experience: how much they reward your time, what they give you that you cannot get anywhere else, and how well they fit into a realistic itinerary. The Alhambra is first because it genuinely is the finest surviving medieval palace complex in Europe. But the cave flamenco performances in Sacromonte, the Hammam baths, the Generalife water gardens, and the tapas crawl through the old city each make a serious case for second place.
Practical note on the Alhambra: book tickets at least 3 weeks in advance for spring and summer visits. The daily limit is strict and the allocation sells fast. There is no same-day queue. If you arrive without a ticket, you are not getting in. Everything else on this list can be arranged within a day or two of your visit, except the hot-air balloon, which depends on weather.