In this talk, I will present a new perspective about decomposing gravitational systems into subsystems. I will explain what is the nature of entanglement of gravitational subsystems and the importance of local symmetries. I will emphasize the central role of the corner symmetry group in capturing all the necessary data needed to glue back seamlessly quantum spacetime regions. I will explain some of the key results we have achieved in the construction of the representations of these groups. If time permits, I will present new results about the canonical description of open gravitational systems and what it teaches us about the nature of quantum gravitational radiation.