I wrote a humour/travelogue book about cycling from Land's End to John O'Groats in the UK, around 1,000 miles or so over 8 days. Self-published on Kindle and did pretty well for a couple of years - proceeds funded a boy's cycling road trip to Sweden for me and my brother-in-law.
Like Dave 90TT I used to be seriously into fantasy/sci-fi and have a series of books partially written sitting on a dusty HDD somewhere. Maybe when I retire I'll go back to it..... don't think it'll ever raise much more than some beer money mind you. George RR Martin it ain't....