The temple of Ramses II is now one of the most famous monuments in the world. The Pharaoh carved it into the rock of the Nile Valley between 1274 and 1244 B.C., and it was saved from being flooded by the waters of Lake Nasser by a frantic international effort in the early 1960s. Three colossal (21m/69-ft.) statues of Ramses II guard the entrance to a temple dedicated to Re-Harakhty, Ptah, and Amun. Around his feet stand his family, including his wife Nefertari. Inside, the temple goes about 60m (200 ft.) back into the rock, passing eight smaller statues of Ramses II and some stunning reliefs proclaiming his military superiority on the way, to an inner sanctuary where there are statues of four seated gods -- Amun, Re, Ptah, and Ramses II himself (who was deified). The whole facility is designed and oriented so that on every February 22 and October 22, the first light of the rising sun shines through the door all the way back to the sanctuary and onto the seated gods (though Ptah actually remains somewhat shadowed). Before the temple was raised up from its original location, this happened 1 day earlier.
There is actually a second temple in Abu Simbel, dedicated to Hathor and also built by Ramses II. It is a little to the north of its more famous counterpart, and about half the size. It is interesting, however, that, in this case, his wife Nefertari is shown the same size as her husband.
Abu Simbel will take a full day out of your schedule if you go by car. If your schedule is tight and this is on your must-see list, consider the flight from Aswan. Though it's expensive (around $150 per person from Aswan), it gets you there in 45 minutes instead of 3 hours. Leaving early from Aswan, the plane will get you back in time to catch many of the cruises out of Aswan that night. Airfare includes the 10-minute bus ride from the airport to the temples. There is a sound and light show at Abu Simbel, but to catch it you have to stay overnight in one of the expensive and bad hotels in the town, which isn't worth it. Spend the time, and money, taking in the show at Philae, and stay the night in Aswan.