A half-day in Aswan pairing the High Dam with a boat ride to the Temple of Philae, built for the goddess Isis on an island in the Nile.
You begin at the High Dam, where your guide explains what it actually changed: electricity generation, year-round irrigation, and an end to the annual flood that Egyptian agriculture had depended on for millennia. From the top there are wide views over Lake Nasser on one side and the Nile on the other, which makes the scale of the thing much easier to grasp than any figure would.
From the dam you transfer to the marina and take a short motorboat across to Philae Island. The temple is one of the loveliest in Egypt, dedicated to Isis, goddess of love and magic, and you have time to walk the courtyards, pylons and inner sanctuaries while your guide sets out the rituals that took place here. There is also the story of how the temple came to be on this island at all: threatened with permanent flooding after the dam was built, it was taken apart and reassembled on higher ground in a UNESCO-led rescue.
After Philae you are driven back into Aswan and dropped at your hotel, with the rest of the day free.