This is Las hurdes or Terre sans pain (1933), by Luis Buñuel. We are going to see it in my class on modern Spanish literature. It is very interesting and engages questions of civilization and barbarism, modernity and the primitive, city and country, center and margin. It is a documentary but as cinematography it is experimental, quasi-surrealistic, theatrical.
I have been to both of the metropoli mentioned here, Ciudad Rodrigo and La Alberca, a very long time ago when Franco was still chief of state. Las Hurdes are just across the border in Extremadura, province of Cáceres.
Buñuel did not come up with this topic on his own; it is a trope. Las Hurdes has been discussed as a place of backwardness and horror since the 16th century. Lope de Vega wrote a play about it and by the time this film was made, it had been defended against accusations of lacking religion by Menéndez y Pelayo. Now it has been the object of several social aid campaigns.
Axé.