Aswan is where Egypt ends and Nubia begins. The Nile breaks over granite here at the First Cataract, which made it the ancient southern border, a quarry for obelisks and a gateway for ivory and gold, and the name of Elephantine Island still remembers the ivory trade. Then the British built the Low Dam in 1902 and the Soviets helped build the High Dam in the 1960s, and the river behind them drowned Nubia. The temples of Philae and Abu Simbel were cut up and moved to survive. Everything you see here is, in some way, about that rescue.
The city has about 350,000 people and feels calmer than Luxor. The corniche is wide, the Nile is a deep blue between granite boulders, and the pressure to buy a calèche ride is lower, though not zero. Three days is the right length: one for the sights south of town, one on the river and islands, and one for Abu Simbel, which takes most of a day however you reach it.
Day one is Philae, the Unfinished Obelisk, the High Dam and the Nubian Museum. Day two is Elephantine Island, the Botanical Island, a felucca and a Nubian village on the west bank. Day three is Abu Simbel. Aswan sits at the far end of an Egypt trip: most people come from Luxor or from Cairo. Every site opens daily, so start on any weekday. If you start on a Thursday or Friday, the Nubian Museum also reopens in the evening.