Nile Alignment
It is likely that the location of nearly all of Egypt’s pyramids is to the west of the Nile in order to allow the dead’s spirits to follow the setting sun. The fact that many of the quarries in the vicinity were on that side of the river didn’t harm either, either.
The Hidden Door
The Great Pyramid, among other architectural marvels, contains a hidden 20-ton door on one side that can be opened only by a special key. It appears to be impossible to move, but clever hinges allow it to be opened with a single push from a single individual.