What it is
On the east bank, Karnak is a temple complex built and rebuilt over roughly 1,500 years, and Luxor Temple sits in the middle of the modern town. On the west bank are the Valley of the Kings, the Valley of the Queens, the terraced temple of Hatshepsut at Deir el-Bahari, the Ramesseum, Medinet Habu and the Colossi of Memnon. A bridge and a constant ferry connect the two.
Why go
This is the core of the trip. The painted tombs in particular hold colour that photographs do not prepare you for. Two full days is workable; three lets you see the west bank properly without doing it in one brutal morning.
When to go
November to March. Start on the west bank at opening, around 6am in summer and 6am to 7am in winter, and be finished by midday. From May to September the site is above 40°C, the tombs are hotter and stiller than the open air, and the walk between them has no shade. Hot air balloon flights go up before dawn and are cancelled in wind.
Most people stay 2-3 nights.