When one embarks upon the unfathomable journey through the interstices of the unseen and the imagined, it is imperative to comprehend that each step taken, each shadow encountered, acts as a reflection of one's own essence cast across dimensions yet undefined. To walk in these corridors of phantoms, one must not only bring a lantern of knowledge but also acquire a mastery of the intricate art of seeing beyond, for the portals that lead through the veils of reality are only visible to those who have learned to listen to the whispers of the forgotten spaces.

Therefore, initiate the journey by understanding the labyrinthine pathways that comprise the very fabric of these ephemeral realms. For instance, the first corridor, known as Ephemeris, demands of you a certain flexibility of mind and spirit, as it is woven with threads of time that twist and curl like the smoke of an ancient sage's incense. Here, one learns that permanence is but an illusion.

As one progresses deeper, the second junction, marked by the sigil of the Immaterium, reveals itself, presenting a conundrum wrapped in riddles and enigmas where the very notion of substance becomes questionable, urging the seeker to ponder the nature of existence beyond mere tactile sensations. It is essential at this crossroads to understand the significance of both presence and absence, for they are two sides of the same cosmic coin.

Finally, as the journey nears its zenith, the third realm introduces the concept of Whispers, a domain where echoes of thoughts not yet spoken reverberate through the void. In this mystic expanse, the portals to other dimensions flicker and fade, inviting those daring enough to step through into unknown possibilities, where every decision, however minute, may alter the course of one's existential trajectory.

Thus, dear traveler, as you traverse these pathways of the phantoms and dimensions, remember always that the true journey lies not in the destination but in the becoming of the self that dares to wander.