Tommy Grahams is the Nullarbor cave rated 'Cave' (rather than Advanced Cave) by the CDAA, but it is no easy dive. The CDAA site description traces a steep entrance slope down a nearly choked rockpile into the main chamber and a small lake, then a 190 m sump through a phreatic maze to an 80 m dry chamber with another lake. Beyond, Glacier Lake leads 130 m to a 30 m-diameter rockpile chamber blocked 35 m above the water.

A TDI trip report adds detail: the first sump reaches an official 30 m depth (the team recorded 36.4 m), with named passages including The Keyhole, The Five Ways, The Blue Room – which has an amazing halocline – and The Slot. The dry 'Inner Sanctum' has high CO2, so divers breathe from their cylinders or rebreathers while crossing. Water and air in the cave are a relatively warm 24°C.

The cave was explored from Christmas 1973/74, with about 1,300 m added in the early expeditions; the final rock pile could not be passed in 1975. Divernet notes that only 50-60 people have reached the furthest point, and that the system may extend for many kilometres.

The entry is brutal – a restriction called The Birth Canal and a 55-degree slope – and the site is remote. Divers must apply to DBCA Esperance four weeks ahead. Teams typically base themselves at Cocklebiddy and allow several days for the hauls, dives and recovery. Rebreathers make the Inner Sanctum crossing and long dives more manageable.

The Nullarbor caves lie along the Eyre Highway between Norseman and the SA border, roughly 11-14 hours' drive from Perth. Cocklebiddy Roadhouse (fuel, meals, water, showers) is the base for the central caves; Norseman, 435 km west, is the nearest regional centre. Access to the cave entrances is by unsealed station/bush tracks (4WD recommended), and all cylinders, compressors, gas, water and rope/hauling gear must be carried in.

From Cocklebiddy Roadhouse, Tommy Grahams is a further 30 minutes by track. The entrance is at about 90 m above sea level, with the water table at sea level: divers crawl through a restriction known as 'The Birth Canal' and descend a 55-degree slope to the lake – a haul one team compared to climbing a 30-storey building, taking four people six hours. DBCA written permission is required.

Surface weather matters mainly for access and safety: summer temperatures can exceed 45°C, making gear hauls dangerous, while winter nights are cold. Heavy rain is rare but can flood entrances and destabilise rockpiles (the 1988 Pannikin Plains collapse followed a severe storm). Underwater conditions are stable year-round: groundwater at about 19°C (24°C at Tommy Grahams), often brackish to saline with haloclines, and visibility commonly 20-50 m or more unless disturbed.

Autumn to spring (April-October) is the usual expedition season. Tommy Grahams' water and dry cave are about 24°C – warmer than the other central caves – and the Inner Sanctum air chamber has high CO2 levels.

Cave-rated divers dive the entrance lake and first sump through the phreatic maze (The Keyhole, Five Ways, Blue Room with its halocline). Crossing the 80 m Inner Sanctum requires breathing from cylinders/CCR because of CO2; the second sump from Glacier Lake runs 130 m to the Terminal Rock Pile.

CDAA Cave rating (Wikipedia/CDAA site list). DBCA Esperance permit, four weeks' notice. Carry gas/CCR for CO2 chamber crossing; plan multi-hour gear hauls.

No operator – CDAA-rated divers by permission only.