hot tub vs massage parlor

hot tub

noun
  • A large tub, often situated outdoors, filled with hot water and used for communal leisure bathing. 

massage parlor

noun
  • A place where clients can pay for a massage. 

  • A place that offers a happy ending (a hand job) after the massage; a front organization for a brothel. 

How often have the words hot tub and massage parlor occurred in a corpus of books? (source: Google Ngram Viewer )