Mythological cosmology in Indo-European traditions represents the universe not as a singular and static structure, but as a multilayered network of sacred realms, spiritual domains, and interconnected planes of existence. Within this framework, Iranian mythology, particularly in Avestan and Pahlavi texts offers a complex conception of the relationship between the material world (gētīg), the spiritual realm (mēnōg), the world of fravašis, afterlife domains, and sacred cosmological spaces that extends beyond a simple material/spiritual dualism. Despite the importance of this structure in understanding Iranian cosmology, most previous studies have focused primarily on religious dualism or ethical oppositions, while the notion of “spiritual parallel worlds” has rarely been examined through a comparative and structural approach. This study investigates the multilayered cosmological structure of Iranian mythology in comparison with Vedic and Norse cosmologies through a descriptive-analytical method grounded in comparative mythology. The research draws upon the Avesta, Bundahišn, Dēnkard, the Ṛgveda, the Upaniṣads, the Poetic Edda, and the Prose Edda, and analyzes them through the theoretical perspectives of Mircea Eliade, Georges Dumézil, and Claude Lévi-Strauss. The findings demonstrate that all three traditions conceive the cosmos as a “multilayered and traversable” structure; however, this model assumes different forms within each tradition. In Iranian cosmology, the structure is shaped by ethical and eschatological dualism; in the Vedic tradition, it is associated with levels of consciousness and cyclical temporality; while in Norse mythology, it appears as a dynamic network of interconnected worlds. The study argues that the concept of “spiritual parallel worlds” may be understood as a shared cosmological pattern within Indo-European traditions, reinterpreted in accordance with the theological and metaphysical worldview of each culture.