Maledette piramidi - Pyramids, by Terry Pratchett (1989, UK)

A disc world novel, set in an Egypt like land: Teppic, although trained as a graduated assassin, is the next Pharao, but there's sth wrong with the pyramids and the time ...the valley of the kingdom switches dimension: a mess of gods and dead Pharaos... Dios the high priest, uncountably years old, hides a mystery and an unusual ending is awaiting. Good.