Rock Cod Cave is a small cave or overhang on the southern, more exposed side of Julian Rocks, close to the better-known Cray Cave and Gorgonian Hollow, and takes its name from a large resident black (rock) cod that has made the overhang its home. Like its neighbours on this side of the island, the site sits at a deeper, more current-affected depth than the sheltered Nursery, generally 18-24 m, and is recommended for Advanced Open Water divers comfortable with moderate current and an overhead-adjacent environment. The black cod itself is the main drawcard: a large, slow-moving resident fish that is usually found tucked into the same overhang on repeat visits, giving divers a reliable big-fish photography subject in addition to the site's other typical residents — wobbegong sharks, moray eels and, in the cooler months, grey nurse sharks using the general area to shelter from current in the same way they do at Cray Cave and the Cod Hole nearby.

Turtles and schooling bullseyes round out a typical dive here. Because Rock Cod Cave sits so close to Cray Cave and Gorgonian Hollow, it is usually dived as part of the same deeper circuit on the southern side of Julian Rocks rather than as an isolated destination, and operators will brief the day's plan based on which of these closely spaced features best suits conditions and diver interest. As with the rest of this exposed flank, a moderate south-easterly swell will make the site unworkable, and it is only run when conditions allow the deeper southern sites generally.

Both Byron Bay dive operators launch small rigid-hull inflatables directly off the beach: Sundive Byron Bay from The Pass, Byron Bay Dive Centre from near Wategos/Clarkes Beach; check in first at the shopfront in town, then walk down to the beach for the boat launch briefing.

Julian Rocks sits fully exposed 2.5 km off Byron Bay; a big easterly or south-easterly swell closes the outer sites but the Nursery side can often still run. Visibility can change from 5 m to 20 m within a single day as warm and cool currents meet around the rocks. Summer (Dec-Mar, 21-26°C) brings leopard sharks and mantas; winter (Jun-Aug, 18-21°C) is cooler but usually clearer, with grey nurse sharks and migrating humpback whales.

Descend to the cave/overhang at 18-20 m, approach slowly to view the resident black cod without crowding it, then continue to the nearby Cray Cave and Gorgonian Hollow if time and gas allow before ascending along the outer wall.

Sundive Byron Bay (The Pass) and Byron Bay Dive Centre (Wategos/Jonson St) both run daily boat dives to Julian Rocks.