This article is about the Deep Grand Reef. You may be looking for the Grand Reef.
Scans show extensive cave networks below the surface in this area, accompanied by unusual energy signatures.
― PDA, Dialogue
The Deep Grand Reef is a large cave system located beneath the Grand Reef, featuring many hydrothermal vents.
Though it lacks the Membrain Trees found in the Grand Reef, it shares the same Anchor Pods. The Deep Grand Reef is considerably more dangerous than the Grand Reef as it is home to many Crabsquids, capable of disabling electrical devices such as Flashlights and vehicles.
Spoiler alert: The following section contains story related material.
At the deepest point in this area, there is an entrance to the Lost River.