A crude stairway cut into the side of the doline leads down to a pool barely large enough for two divers, and the dive begins with a duck-under beneath the rock into a steeply sloping cave roughly 80 m long. The slope runs down to a maximum depth of about 24 m, where a large chamber gives plenty of room to look around.

The floor is rubble and loose rock covered in a deep layer of dark brown silt, and that defines the dive. On the way down the slope the water can be clear, but any contact with the floor or careless finning sends clouds of brown silt downhill and uphill, and the exit then has to be made on the line in poor visibility. The CDAA listing stresses care to prevent silting, and the site makes an excellent test of frog kick, trim and line handling for newly rated Cave divers.

It is not a scenic showpiece – no decorations, little life and a gloomy colour palette – but it is close to Mount Gambier, needs no complicated booking (just the key from the Lady Nelson Visitor Centre), and gives a genuine overhead-environment dive with a real depth profile. Only two keys exist, so plan around other teams, park off the road, and keep the gate locked while in the water. It suits CDAA Cave-rated pairs looking for a quick, technical skills dive on the way to or from the Port MacDonnell area.

Collect the site key (only two exist) from the Lady Nelson Visitor Centre, 35 Jubilee Highway East, Mount Gambier, during business hours. Drive about 20 km south to Allendale East; the cave is in the township, formerly known as 'Middle of the Road'. Park on the grassed area to the south-west, well off the road, unlock the gate and keep it locked while diving.

Carry gear to the doline and down the crude stairway cut into its side – a rope is often needed as it is steep and slippery – to a pool just big enough for two divers. Return the key afterwards (after-hours return available).

Unaffected by swell or wind. Rain makes the cut stairway treacherous and can wash surface debris and silt into the small pool; the doline is sheltered but the key must be collected during Visitor Centre business hours, which effectively limits dives to daytime. Constant ~15°C water.

Avoid diving immediately after heavy storms, when the pool clouds.

Two divers kit up in the small pool, run a primary reel from outside the duck-under, pass beneath the ledge and follow the steep rubble slope down to the chamber at about 24 m. Explore the chamber carefully, turn on thirds, and ascend the slope keeping well off the silt; the whole cave is about 80 m long.

CDAA grade: Cave (5L11), owner Port MacDonnell (District Council of Grant). Continuous guideline from open water through the duck-under; rule of thirds; three lights; nitrox 32% suitable for 24 m. Max two divers at the entry pool at once.

No commercial operator – CDAA Cave-rated members self-organise using the key system; occasionally used on CDAA Cave courses.