Proposal
Your list books become lists in the app. People tick off places as they travel, build a passport of stamps and badges, and see how their friends are doing. A code inside each book unlocks its list, so every book sold brings a reader into the app, and every app user has a reason to buy the book.
How it fits in with your current app
Lists sit under Guides next to your city guides. Each list has three tabs: the list, your passport and the community. Every place page gets one new option alongside the heart and Add to trip: Been, with a date and a rating. City guides get the same for their top sights.
About this page
Click through the app to see a rough demo of how this could look in your app. It uses sample data; reset the demo to start again.