Deep Glen Bay cuts into the Forestier Peninsula north of Pirates Bay, and its northern side forms a wall that is one of the most frequently dived sites on this stretch of coast. Local photographers describe it as a 'Sisters lite': the wall merges into the coastline and carries colourful sponges, sea whips and invertebrates, but it sits in a more sheltered position, so it is the site operators use when the weather is not cooperating offshore. Go Dive Tasmania rates it at 10-40 m with sheer walls, excellent visibility and a good chance of weedy seadragons, while the Marine Life Network guide describes a reef extending seaward with narrow ledges and caves, sponges, hydroids and gorgonians in about 30 m.

The Tasmanian Scuba Diving Club notes steep underwater cliffs, boulder fields and kelp forest. The Divers Alert Network's account of diving here with Mick Baron and Karen Gowlett-Holmes singles out the North Wall's tapestry of invertebrates and fish, including Shaw's cowfish, banded morwong and rock lobster. New Zealand fur seals are regular visitors, weaving through the kelp at the top of the wall.

The flexibility of the site is its strength. Newer divers can stay at 12-18 m along the upper wall and still see plenty of colour, while Advanced and Deep divers can drop to 30 m and beyond where the sponge and sea-whip gardens become denser. Weedy seadragons are found on the kelp and sand edges in the shallower sections.

Visibility is often excellent because the site is washed by clean coastal water. It is a reliable, varied dive that many visitors end up doing more than once.

Boat access only. Eaglehawk Dive Centre's catamaran and Go Dive Tasmania's boat leave from the Pirates Bay jetty/boat ramp at Eaglehawk Neck (Old Jetty Road, off the Arthur Highway about 75 km and 1 hour 15 minutes from Hobart). The Forestier Peninsula sites lie north-east of Pirates Bay: the run across the bay and around Cape Surville takes roughly 15-25 minutes depending on sea state.

Private boats also launch at Pirates Bay; there are no public moorings on the offshore pinnacles, so boats drift-dive or anchor in sand well clear of sponge gardens and run a live-boat pick-up.

The Forestier Peninsula coast faces east and north-east into the Tasman Sea with no shelter from easterly weather. These sites need westerly or north-westerly winds and small swell (generally under about 1.5 m) from the east and south-east; north-easterly sea breezes that build through summer afternoons often shut them by midday, so trips run in the morning. Southerly groundswell wraps around Cape Surville and creates heavy surge on the shallow tops.

Currents are unpredictable and can run strongly around the points and pinnacles, especially on spring tides and when the East Australian Current pushes south in late summer. Autumn (March-May) gives the most frequent calm windows and the clearest water; operators decide on the morning of the dive. Deep Glen Bay is more sheltered than the Sisters and is often still diveable when the offshore pinnacles are not.

Descend on the wall at its seaward end, drop to the depth that suits the group (18-25 m for most, deeper for Deep-certified divers) and follow the face into the bay. Check ledges and caves for cowfish and lobster, and rise through the kelp at the inner end for a safety stop.

Eaglehawk Dive Centre – regular site and the usual alternative when the Sisters are too rough; Go Dive Tasmania – Deep Glen Bay (10-40 m, Open Water to Deep); Tasmanian Scuba Diving Club – club trips.