Beautiful coral reef
A visit to the red sea is a "must" for people who like the sea and snorkelling, because there you can really swim with many wanderful and multicoloured fishes. You even learn to recognise them!
But you have to be aware that there's nothing but the desert. So I think 1 week is the maximum time to spend there.
Your tour operator will offer you many excursions, as there's nothing to do except snorkelling!! Usually the most agreable trips are:
-excursions on a boat to places where you can see sea animals like turtles and sea cows
-visit to Luxor (in my opinion this journey is too tiring because you are supposed to wake up at 3 in the night and come back late the following night, but the visit to the piramides is short)
-visit to a local village
-trip in the desert with the quad. I did this and it was amazing. We stopped in a bedouin tent to drink a tea and see the sunset