This paper presents Goliath footbridge, a full-scale 6 m span segmental 3D-printed concrete footbridge activated by post-tensioning, describing the end-to-end process from design and fabrication to transport, assembly, and structural activation. This structure represents the demonstrator of a research project that was conceived as an end-to-end demonstrator integrating material development, digital design, additive manufacturing, and site erection. The printable mortar was previously characterized through rheological and mechanical tests to verify extrusion performance, buildability, and strength development. The structural geometry was obtained through topology optimization under self-weight and pedestrian service loads, aiming to maximize stiffness and reducing material consumption. The resulting solution provided an efficient lightweight configuration adapted to additive manufacturing. After production, the segments were transported to site, rotated into their final position, assembled on temporary supports, aligned through the dry-joint system, and sequentially activated by post-tensioning. The demonstrator confirmed the technical feasibility of combining topology optimization, modular 3D concrete printing, dry-joint assembly, and post-tensioning for pedestrian bridge applications. It also highlighted practical challenges related to dimensional tolerances, local stress concentrations, cracking sensitivity, and durability of joints and anchorage zones. The study provides a practical proof of concept for future scalable 3D-printed concrete bridge construction.