In 'The Riddle of the Universe at the close of the nineteenth century', Ernst Haeckel delves into the mysteries of existence and the universe with a scientific and philosophical lens. Published in 1899, the book explores the intersections of science, religion, and philosophy, offering a comprehensive look at the fundamental questions that have puzzled humanity throughout history. Haeckel's writing style is both articulate and thought-provoking, drawing upon his background as a renowned German biologist and philosopher to provide insightful commentary on the evolution of life and the universe. The book is a significant contribution to the academic dialogue of the time, influencing later thinkers and scientists in the fields of cosmology and evolutionary biology. Ultimately, 'The Riddle of the Universe' serves as a compelling exploration of the complexities of existence, challenging readers to contemplate the profound mysteries of the universe.