Augmented Reality (AR) and Virtual Reality (VR) users have distinct capabilities and experiences during Extended Reality (XR) collaborations: while AR users benefit from real-time contextual information due to physical presence, VR users enjoy the flexibility to transition between locations rapidly, unconstrained by physical space.Our research aims to utilize these spatial differences to facilitate engaging, shared XR experiences. Using Google Geospatial Creator, we enable large-scale outdoor authoring and precise localization to create a unified environment. We integrated Ubiq to allow simultaneous voice communication, avatar-based interaction and shared object manipulation across platforms.We apply AR and VR technologies in cultural heritage exploration. We selected the Euston Arch as our case study due to its dramatic architectural transformations over time. We enriched the co-exploration experience by integrating historical photos, a 3D model of the Euston Arch, and immersive audio narratives into the shared AR/VR environment.