a walk in the park vs plain sailing

a walk in the park

plain sailing

noun

  • The navigation of waters free from hazards or unfavourable winds. 

  • Something that is simple, straightforward, or easy; something that offers no troubles or difficulties. 

adj

  • simple, straightforward, or easy 

How often have the words a walk in the park and plain sailing occurred in a corpus of books? (source: Google Ngram Viewer )