Shortly after the Christmas Foundation Conference of 1923-24, Rudolf Steiner inaugurated the First Class of the School of Spiritual Science, presenting a cycle of nineteen lectures, featuring mantras and blackboard drawings, intended to guide the modern seeker on the contemporary path of inner development. These Esoteric Lessons remain among the most intimate and challenging teachings Steiner ever gave. In Know Yourself, Journeys Between Worlds, Maarten Ploeger offers a unique and deeply personal response to this spiritual legacy. Through a series of imaginative dialogues, reflections and poetic meditations, he accompanies the reader on an inner journey inspired by Steiner's mantras. A 'traveller' and his wiser 'companion' - the alter ego - explore the thresholds between the visible and invisible worlds, while a higher guiding presence, the 'Voice of the I', gradually reveals the deeper nature of the human being and the path toward self-knowledge. Rather than explaining the Esoteric Lessons intellectually, this book seeks to illuminate their living, experiential dimension. The accompanying reflections deepen the themes encountered along the way, while three lyrical 'Songs' mark key stages of the soul's journey. Both contemplative and inspiring, Know Yourself invites readers to enter more deeply into Steiner's path of self-discovery and the timeless quest to know the true Self.