The rariphotic zone (130–300 m) and the Deep Sea beyond remain some of the least explored marine frontiers, harbouring unique, often undiscovered biodiversity. These depths, where sunlight fades and pressure rises, reveal resilient coral ecosystems, bioluminescent life, and species adapted to extreme conditions. Advanced technologies like ROVs and submersibles are uncovering their mysteries, offering insights into climate resilience, deep-sea refugia, and the hidden dynamics of marine ecosystems. As climate change threatens shallower reefs, understanding these deeper habitats is crucial for conservation and future discoveries.