Naples is significant to Jane Eyre because it represents two juxtaposing ideas: beauty and temptation. This information comes from the academic blog: "Re-thinking Tourism: visitors to nineteenth-century Naples and the consumption of feeling." Within the novel, Naples represents the two sides of marriage. In chapter 24, Mr. Rochester tells Jane that they will go to Naples for their honeymoon. In this context, Naples represents a beautiful place where Jane will enjoy bliss and constant tranquility after she gets married. In chapter 27, Mr. Rochester reveals that he often went to Naples to seek mistresses, blatantly disrespecting and disregarding his wife. In this context, Naples represents temptation and adultery. Mapping Naples on COVE reveals the reality of marriage, and the dark sins that can be hidden behind a beautiful exterior. 
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Photo: https://monovisions.com/historic-bw-photos-of-naples-italy-in-19th-century/