There has been some discussion on the EEF lists the past couple of days on the “Giza caves” which I had never heard of. Turns out they were discovered (well, excavated/explored) by Hawass in 1999. Called the Shaft of Osiris it’s been flooded since. . .well, it doesn’t say since when, but presumably since the Aswan dam was built and the water table rose accordingly, I would think. turns out to be a pretty big complex. He mentions Herodotus naming it as the burial place of Khufu, but they found mostly remains from the Late period, and a few sherds which may be Old Kingdom. I wouldn’t rule it out as Old Kingdom in origin; it certainly could have been reused in later times after having been largely cleared of earlier remains.
But I thought that was way cool.
UPDATE: Also see Al Ahram’s article on Abydos.