Though the main stories of The Lord of the Rings and The Hobbit are riveting enough on their own, some of the most interesting stories in Middle-earth are the ones that aren't found within those main books and are instead parts of the overall lore that Tolkien expanded upon in other books or just in his notes. The origins of Middle-earth and beyond are fascinating, as these stories aren't exactly integral to the plot of The Lord of the Rings, but are detailed enough that they could have become whole books on their own.