Mandeville Road is the name Scuba Doctor gives to the reef off the southern shore of Phillip Island's Summerland Peninsula, west of the Penguin Parade, after the old subdivision road that once ran to the coast before the houses were bought back and the peninsula returned to the penguins. The listing describes an impressive reef dive of large basalt formations, dramatic underwater canyons, bommies and gullies about 200 metres offshore, in 2–12 m. It is, in other words, the same columnar basalt that forms Pyramid Rock and the south-coast headlands, but here fractured into a maze of vertical-sided channels and free-standing blocks that a diver can swim through and around.

The canyon walls carry kelp on their rims and sponge, zoanthid and ascidian growth on their shaded faces; the floors are cobble and sand; and the bommies rise to within a few metres of the surface, where surge keeps them scoured. Marine life is not detailed on the listing, but the habitat is the same as Phelan Bluff a kilometre east and the neighbouring shore reefs – crayfish and abalone in the cracks, Port Jackson and draughtboard sharks in the gutters, blue devils and bullseyes under overhangs, and morwong, sweep, wrasse, boarfish and old wives over the reef – with fur seals from Seal Rocks, 3 km west, likely visitors. What sets the site apart is its combination of shallow depth and severe exposure.

There is no shore access because the peninsula is a closed penguin reserve, the reef faces directly into Bass Strait, and a boat has to come around The Nobbies or along the whole south coast to reach it, so it is dived only by private boats on exceptionally calm days. When those days come, the canyons in clear shallow water make a spectacular and photogenic dive, and the reef sits in a piece of coast that very few people ever see from the water. It requires a high level of experience and caution, as the listing says, more for the sea state and the boat handling than for the depth.

Boat access only. The nearest ramps are Cowes (Mussel Rocks) and Rhyll on the north coast; from Cowes it is about 15 km and 30–40 minutes west around Point Grant and The Nobbies, crossing the tidal race between The Nobbies and Seal Rocks near slack water, then east along the exposed south coast. From Newhaven the run west along the south coast is about 25 km.

Anchor in sand outside the reef in 12 m. Shore access is prohibited: all off-track areas of the Summerland Peninsula are closed to protect little penguin burrows.

Scuba Doctor describes a high energy open sea zone prone to all of the vagaries of changing Bass Strait conditions and very exposed to southerly swells; the site needs several days of calm weather with offshore northerly winds and a swell well under 1 m, entering at high tide. The boat run around The Nobbies adds a tidal constraint: the passage between Point Grant and Seal Rocks runs hard and should be crossed near slack. Late summer and autumn give the best chance.

Not a winter site.

Anchor outside the reef in 10–12 m and descend the line. Work inshore through the canyons and gullies between the basalt formations, keeping the boat's bearing, explore the bommies at 6–10 m, and turn at half gas or when surge in the shallows becomes uncomfortable. Return along the outer edge of the reef to the anchor and complete a safety stop on the line.

Avoid the surf zone inside 4 m.

No regular operator – private boats and Melbourne club boats on rare calm days only.