This thesis delves into the profound intersection of architecture, ritual, and sensory experience in the Eleusinian Mysteries and the Oracle at Klaros. Through meticulously examining archaeological evidence, literary sources, and climatic considerations, the study unfolds the architectural designs of the Telesterion in Eleusis and the Temple of Apollo in Klaros, focusing mainly on the Late Hellenistic to Imperial Roman era. The experiential aspects of these sacred spaces, including spatial distortion, lighting effects, and climatic conditions, are scrutinized for their impact on participants. In Eleusis, the Telesterion's near-symmetrical layout creates an immersive environment, intensified by tiered seating and artificial illumination during the nocturnal ceremonies. The Anaktoron adds a layer of sensory triggers, prompting contemplation on the involvement of deities like Demeter. Meanwhile, the Temple of Apollo and subterranean adyton present a unique architectural ensemble. The labyrinthine corridors, deliberate darkness, and altered atmospheric conditions contribute to a transformative sensory experience. The journey through the crypts involves challenging descents, limited movement, and a revelation chamber. This analysis unveils the profound impact of Eleusinian and Klarian spaces, where the confluence of architectural choices and environmental conditions intricately shapes both initiatory and oracular experiences. The overarching objective of this study is to enhance our understanding of the experiential essence inherent in religious settings. It contributes significantly to a comprehensive knowledge of ancient sacred spaces, portraying them as multidimensional realms where architecture, climate, and sensory manipulation intertwine. This intricate interplay serves as a catalyst, facilitating a profound and meaningful connection between humanity and the divine.