The Book of Lost Tales Part 1" is the first volume of a two-part collection of unpublished stories and drafts written by J.R.R. Tolkien, edited by his son Christopher Tolkien. The book was first published in 1983 and contains several early versions of stories that would eventually become part of the legendarium of Middle-earth.

The book begins with an introduction by Christopher Tolkien, which provides background information on the stories included in the book and the process of compiling them. The first part of the book focuses on the creation of the world of Middle-earth, with a series of stories called the "Music of the Ainur" describing the creation of the universe by the gods.

The book then continues with the story of the Elves and the Valar, the gods of Middle-earth. The story is told through the character of Eriol, a mortal man who stumbles upon the island of Tol Eressea and is told stories by the Elves who live there. These stories include the tale of the first Elves, the love story of Beren and Luthien, and the creation of the Dwarves.

One of the most interesting stories in the book is "The Cottage of Lost Play," which tells of Eriol's encounter with a group of fairies who reside in a magical cottage. The fairies tell Eriol the story of how they came to be in Middle-earth and their relationships with the Elves and Men.

Another highlight of the book is the inclusion of Tolkien's early drafts of the story that would eventually become "The Fall of Gondolin," which was published posthumously in 2018. The drafts show Tolkien's creative process and how he developed the story over time.

Overall, "The Book of Lost Tales Part 1" provides an insightful look into the early stages of Tolkien's world-building and the evolution of the stories that would become the foundation of Middle-earth. The book is a must-read for any fan of Tolkien's work who wants to gain a deeper understanding of the author's creative process and the history of Middle-earth.