In a small village in a valley everyone who reaches the age of 70 must leave the village and go to a certain mountain top to die. If anyone should refuse they would disgrace their family. Old Orin is 69. This winter it is her turn to go to the mountain. But first she must make sure that her eldest son Tatsuhei finds a wife.
The short review is "life's a bitch, then you die" LOL, that doesn't do this absolutely brilliant film any justice, though.
Imamura has crafted a rather sardonic, brutally honest mirror of humans. Like humans, it is both hard to watch, and simultaneously invokes emapthy. Few directors every achieve this level of mastery of the audience's emotions. It holds a well-deserved Palme d'Or.
The legend upon which the movie is based is called Ubasute (姥捨て) in Japanese, or "abandoning an old woman". There is no evidence of it ever being a common practice, though it's a persistent myth in Japan. One of the very plain statements of the director, is that Ubasute reflects the way contemporary Western culture treats it's elderly. In the USA, at least, nursing homes substitute for Narayama mountain.