"A Letter to the Luminous Deep: 1 (The Sunken Archive)" by Sylvie Cathrall is a fantasy fiction novel published by Orbit in 2024. The trade paperback format features 400 pages filled with an epistolary style narrative centered around a letter to the luminous deep. With a captivating storyline and intricate illustrations by the author, this book is sure to engage readers in a world of fantasy and historical themes."