The Gantry sits on the western side of South Solitary Island directly below its historic lighthouse, first lit in 1880 and one of the more remote and evocative lighthouse stations on the NSW coast, and takes its name from the supply gantry crane once used to winch stores up the cliff to the keepers stationed there. At some point the crane structure gave way and fell into the sea below, and its wreckage — now heavily encrusted with decades of coral and sponge growth — forms the backbone of what is today a shallow, sheltered and easy dive site in about 12-15 m of water. Because it sits on the more protected western flank of the island, the Gantry is rarely affected by the swell that can shut down the more exposed north-eastern moorings, and its shallow depth makes it an easy, low-stress site suitable for less experienced divers or as a relaxed final dive of the day.

Turtles frequent the area, wobbegong sharks lie among the wreckage and surrounding rock, and schools of bullseyes and other reef fish have colonised the collapsed structure much as they would a purpose-built artificial reef, while nudibranchs and moray eels occupy the smaller crevices. The historical association with South Solitary Island's lighthouse — a heritage-listed structure still visible from the water — gives the Gantry a point of interest beyond its marine life, and the site is often mentioned by visiting divers and journalists writing about the island as a memorable, easy dive that rounds out a day otherwise spent chasing grey nurse sharks and current on the more demanding sites. It remains, however, a site with more anecdotal than formally documented detail, and exact figures on depth and extent should be treated as approximate.

Jetty Dive Centre departs from a public floating pontoon wharf on the Coffs Harbour boat harbour, opposite the Attitude Burgers building — check in first at 398 Harbour Drive, Coffs Harbour. It is roughly a 30-40 minute run out to South Solitary Island, 8 km offshore, in the dive centre's RIBs. Private boats launch at the Coffs Harbour public boat ramp inside the breakwall and follow the same course out past the harbour entrance.

South Solitary Island sits in open water 8 km off Coffs Harbour and is exposed to swell from the north-east through south-east; Jetty Dive Centre generally wants under about 1.5-2 m swell to run the outer moorings comfortably, switching to the more sheltered Split Solitary Island (only 20 minutes out) on rougher days. Visibility here is usually the best in the marine park given the distance from any river mouth, and the site's position at the boundary of tropical and temperate water means conditions can change quickly with wind shift. Summer (Nov-Apr) water is warmed by the East Australian Current to up to 26°C, bringing tropical fish, manta rays and, from December, leopard sharks; winter (May-Oct) cools to about 18°C but often gives calmer seas, giant cuttlefish and the peak grey nurse shark season (Jun-Nov, sometimes 30-60+ sharks on Manta Arch).

Humpback whales migrate past between April and November, peaking June-August northbound and September-November southbound. Currents can run strongly on the exposed north-eastern moorings (Manta Arch, Shark Gutters) and are much gentler on the sheltered north-western wall.

Descend below the lighthouse cliff to the gantry wreckage at 12-15 m, explore the collapsed structure and surrounding reef looking for turtles and schooling bullseyes, and finish shallow near the base of the island for the ascent.

Jetty Dive Centre (Coffs Harbour) runs South Solitary Island most days conditions allow, typically a double boat dive; it is the flagship site for the only major dive operator based in Coffs Harbour.