purgatory vs underworld

purgatory

noun
  • Any situation where suffering is endured, particularly as part of a process of redemption. 

adj
  • Tending to cleanse; expiatory. 

underworld

noun
  • The world of the dead, located underneath the world of the living; the afterlife. 

  • That part of society that is engaged in crime or vice. 

  • The portion of a game that is set below ground. 

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