Obelisk Beach is the southern of Middle Head's two little naturist beaches, a pocket of sand below the bushland of Sydney Harbour National Park looking across Obelisk Bay toward Chowder Bay and Georges Head, named for the navigation obelisks on the ridge above. Vizzbud describes it as 'a calm, easy dive best suited to beginners', mostly sandy with scattered rocky sections, stingarees on the sand, pipefish in the seagrass and small reef fish, and recommends it for training, refresher and navigation practice; it is frequently combined with Cobblers Beach on the northern side for a two-dive day. The VIZ club's Middle Head survey adds the important detail that the sand line east of the beach at 8–10 m leads along the north-east segment of the head to the sponge gardens, large boulders, crevices and swim-throughs that are the best of Middle Head.

Close to the beach the dive is sand, seagrass and small rock with stingarees, pipefish, flathead, octopus and the odd seahorse; further east it becomes a proper reef with sponges and ascidians on the boulder faces, Port Jackson and crested horn sharks under them, blue groper, yellowtail schools, red morwong and, in the club's logs, sea turtles, lobsters and hammer octopus. The Beehive Casemate mine tunnel lies along the same face for those who know where to look. The cost is the steep path with gear and the naturist etiquette of the beach; the reward is a quiet, sheltered dive that scales from a beginner's sand paddle to a 450 m reef traverse.

It suits new divers, navigation students and night divers, and the VIZ club's map is the guide to have. Details from Vizzbud should be confirmed on site; the VIZ survey is the more reliable source.

From Mosman take Middle Head Road to the small car park at its end (NPWS, limited spaces) or park along Chowder Bay Road near the Obelisk Beach track head. A steep stepped bush path drops about 37 m to the beach – shorter than the Cobblers track but steeper, 'nothing particularly hard' according to the VIZ club but a chore with gear. Enter from the sand; the sponge gardens lie east along the sand line toward the head, and the Beehive Casemate cutting is further along the same face.

Exit onto the beach and climb out.

Sheltered from swell inside the harbour but facing south-east toward the Heads, so a very large southerly swell puts a little surge on the beach and along the face; otherwise weather-proof. Visibility 4–6 m, better on a winter flood, poor after rain. Boat traffic into Chowder Bay and around the head is heavy on weekends – stay on the sand line near the rocks.

Enter from the beach, cross the sand and seagrass at 3–5 m looking for stingarees and pipefish, then follow the sand line east along the rocks at 8–10 m toward the head for up to 450 m through the sponge gardens and swim-throughs, turn at half air and return along the same edge to the beach.

No operator; VIZ dive club, independent divers, occasional Plunge Diving or Dive 2000 navigation dives.