A day trip to Luxor is very doable but a bit long. Tour companies can pick up up and drop you off at the airport, which makes it doable, just make sure you squeeze in breakfast somewhere-- the tour guide in Luxor had an excellent breakfast place which definitely helped!
The day properly starts off at the Colossi of Memnon, two massive statues of the Pharaoh Amenhotep III. Like many structures dating back to ancient times, both have been badly defaced. The west (south) colossus is a single piece of stone, while the east (north) colossus is actually several tiers. Earthquakes soon after these were constructed apparently buried much of the remaining temple.
Mortuary Temple of Hatshepsut was the next stop. The Mortuary Temple of Hatshepsut is still undergoing excavation, but what you can see now is no less impressive. The damage inflicted by Thutmose III does little to hide that Hatshepsut is one of the most significant queens of Ancient Egypt.
Next stop was Valley of Kings-- unfortunately I did not purchase a photography permit, which was a critical mistake. You get to visit three tombs on the standard ticket; the guide recommended I visit Merenptah, Rameses III, and Rameses VIII. Merenptah (KV8) was the first, a surprisingly large burial chamber with not one but originally four nested sarcophagi inside. The tradition of baksheesh was also well alive inside, with plenty of tourists allowed inside the restricted areas for tips. The tomb Ramesses III (KV11) is better protected from such abuse, and the artwork inside is colorful, spread over multiple rooms as you descend. The tomb of Rameses IX (KV6) was the final stop, with high ceilings and again, plentiful art and hieroglyphs. Truly a place to experience; even outdoors, which is both less and more impressive than one might expect, is alive with active archaeological expeditions-- super cool.
Luxor Temple was the next stop. Located smack in the middle of the city, with obelisks and columns and, at this time of day, sunrays shining through some of the rooms, illuminating the hieroglyphs. It is more approachable in scale than the Valley of Kings or the Mortuary Temple of Hatshepsut, as is the Avenue of Sphinxes that connects it to Karnak Temple Complex. It also feels more alive, not only in the middle of the city but due to constant use by locals and tourists alike.
The walk to Karnak Temple Complex is pleasant in winter, probably not something you'd want to do in the summer. It feels a little like Ancient Rome in scale, but owing to thousands of years more destruction, it is not nearly as imposing. The Great Hypostyle Hall in the Precint of Amun-Re is definitely the highlight, although the Gate at Karnak, Obelisks of Hatshepsut, and the Sacred Lake are all integral parts of the temple to this day. Ruins populate much of the landscape, giving a sense of solitude that must be rare during high season.
A very late lunch/early dinner turned out to be at a restaurant/hotel the tour company owned (sigh). Stuffed pigeon is definitely tourist food, sigh. And while the tour was supposed to be 10 hours long according to their website, the actual plan was only 7 hours. Even stretched out with the walk from Luxor Temple to Karnak, it was still only 8 hours, and throwing in lunch... well, still left plenty of time to head to the airport. At least I got some glimpses of local Egyptian life on the way back to the airport, and the green farms surrounding Luxor were a welcome contrast to the urban dust of Cairo.