mystery tour vs outing

mystery tour

noun
  • A short-duration outing by coach to a destination that is not revealed in advance 

outing

noun
  • A pleasure trip or excursion. 

  • A performance in public, for example in a drama, film, on a musical album, as a sports contestant etc. 

  • The practice of publicly revealing that a person is homosexual or transgender without that person's consent. 

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