The Grand Reef offers a vast open space for exploration. Take advantage of the opportunity to swim with massive schools of fish, ride larger creatures like manta rays, and discover hidden caves and coral formations. This area is rich with fish pools and meditation statues.
Your primary goal here is to locate several more small robots and guide them to a central mechanism, often a large, ancient structure. The scale of this area can be overwhelming, so use the schools of fish as a general guide if you feel lost.