dungeon vs gulag

dungeon

verb
  • To imprison in a dungeon. 

noun
  • A room dedicated to sadomasochistic sexual activity. 

  • An area inhabited by enemies, containing story objectives, treasure and bosses. 

  • An underground prison or vault, typically built underneath a castle. 

gulag

verb
  • To compel (someone) into a forced labour camp or a similar place of confinement or exile. 

noun
  • A prison camp, especially one used to hold political prisoners. 

  • Also GULAG: the system of all Soviet labour camps and prisons in use, especially during the Stalinist period (1930s–1950s). 

  • A place where, or political system in which, people with dissident views are routinely oppressed. 

How often have the words dungeon and gulag occurred in a corpus of books? (source: Google Ngram Viewer )