We investigate the role of the observer, measurement, and accessibility within the framework of Universal Modular Dynamics (UMD), where physical structure is defined in terms of the density operator ρ, its modular generator K = −log ρ, and the associated spectral distribution p(k). In contrast to conventional approaches, where the observer is treated as an external entity and measurement as a distinct process, we develop a structural interpretation in which both arise from the internal organization of the system. We show that the observer can be represented as a localized, stable configuration of the spectral distribution, while measurement emerges as a consequence of limited accessibility to the full structure. In this framework, observable reality corresponds not to the complete structure, but to its accessible projection. The analysis demonstrates that state reduction, information loss, and decoherence can be understood as manifestations of a single mechanism: the restriction of access to the full spectral organization. These results provide a unified structural interpretation of observation and measurement, eliminating the need for additional postulates. They also suggest that classical reality arises as a stable, accessible description of an underlying, more complex structure. The present work completes a sequence of studies in which structure, boundaries, and accessibility are successively derived within a common framework, and establishes observation as an intrinsic process through which structure becomes accessible to itself.