The experience of encountering a reality that transcends both sensory perception and rational cognition—a reality that is “hidden” or “unseen” (al-ghayb)—is among the most complex and, at the same time, most profound dimensions of religious life as it appears within the architecture of sacred spaces. In Twelver Shiʿi thought, the Sacred Mosque of Jamkaran, as a place between a mosque and a shrine, has taken shape beyond a purely devotional site and as an ontological axis rooted in the profound belief in the hidden presence of Imam al-Zaman (may God hasten his reappearance). This research seeks to answer the fundamental question of how the architecture of this mosque provides the ground for the pilgrim’s experience of bringing the Unseen into presence. The method of this research is descriptive-analytical from the perspective of contemporary phenomenology, with a focus on the aesthetics of atmosphere, and has been conducted through documentary and library-based research. To answer the question, the study examines the concept of al-ghayb (the Unseen) in Islamic thought; then it considers the experience of the Unseen on the basis of the theories of the phenomenologist of religion Rudolf Otto; next, it reviews the theories of thinkers concerning the Unseen in sacred space; and finally, it investigates the sensory language of the presence of the Unseen in places by introducing the theory of atmosphere, so that, through linking these concepts, the Unseen—which is essentially imperceptible—can be rendered intelligible. On this basis, Jamkaran Mosque was analyzed. The analysis was carried out through a phenomenological interpretation of meaning. Avoiding any survey, interview, or quantitative measurement, this research seeks to access the existential structure of the experience of the Unseen in Jamkaran Mosque from within the phenomena themselves and to articulate it within an integrated theoretical framework composed of Islamic thought and contemporary phenomenological philosophy. According to the analysis, Jamkaran Mosque encompasses three atmospheres: the sacred (as a space between mosque and shrine), expectation (through liminality), and the Unseen (through the absence of the zārīḥ and related elements). The findings show that the Unseen in Jamkaran Mosque is not produced through a material and tangible symbol such as the zārīḥ; rather, it appears through the absence of bodily presence, the orientation of the building, its symbolic qibla-centered configuration, the rhythm of supplication and prayer, light, silence, and the synchronized movement of pilgrims. In fact, this spatial structure creates an architectural setting in which the pilgrim, in addition to believing in the Unseen, experiences it as a living, immediate, and fully apprehended reality.