Several years ago I started a long-term goal to read a book about every state in the USA. And if every state, why not also territories as well?  That turned into a larger goal to read a book about every nation in the world. Which then needed to include a book for areas that were culturally and/or geographically distinct but not politically autonomous (e.g. Greenland, Antarctica, etc.). Then I realized that too many English language books are set in the same few countries (the UK, USA, Canada, France, Italy, etc.), but generally in the same areas of those relatively large and diverse countries. So then I had to expand my goal to include different states/ provinces/ territories of those countries. This has become an enormous and very long term goal, but I am working at it, and will conquer it eventually. You might call it my bucket list.