Meet the site
The Castle is one of the three sites featured in the Parks and Wildlife Service brochure for the Governor Island Marine Reserve and is rated by the Marine Life Network guide as one of the best dives in Tasmania. It is formed by two massive granite boulders sitting close together against the reef, with a passage between them that Michael McFadyen describes as more of a tunnel than a cave. The tunnel is about 30 m long at around 25 m depth, and there is an alternative route along the outside of the wall for those who prefer not to go through.
The approach is dramatic. From the reef top the dive drops south over a wall to a large overhang about 30 m long and 1-2 m high, then turns west to the tunnel. Inside, the walls are lined with sea whips, yellow zoanthids and jewel anemones, and the tunnel is known for its crayfish, including some very large animals. Schools of bullseyes and cardinalfish hang in the shade, while banded morwong, long-snouted boarfish and butterfly perch surround the boulders. Large bastard trumpeter, abalone in the corners, small gorgonians and yellow sea spiders complete the list.
Beyond the tunnel is an inverted L-shaped indent filled with large boulders, cracks and further swim-throughs, then a kelp-filled crack leads back up to the reef. In calm seas the dive can finish on Mount Everest, a pinnacle that rises to within about 5 m of the surface and gives a colourful safety stop.
The Castle is a dive most visitors want to repeat, because there is too much to see in one visit. It suits advanced divers comfortable with depth and short overhead sections. The tunnel is wide and has light at both ends, but it should be avoided in surge, and divers should keep their fins off the delicate growth.
Research this site before booking Stored site notes may be historical. These questions highlight gaps without turning old instructions into a current dive plan.
The Castle (Bicheno) is recorded as Cave/Cavern in Tasmania East Coast. The listed access is boat (day trip). Confirm the actual meeting point, route and permission to visit; a map pin does not establish any of these.
Topics flagged by the stored research
These are questions prompted by the existing notes, not a verified or complete hazard assessment.
- Other water users
- Ask about vessel activity, exclusion areas and the agreed surface arrangements.
- Planned depth
- Confirm the intended route and training requirements; the recorded maximum is not a target.
- Water movement
- Ask how swell and local exposure affect the proposed entry, exit and route.
- Overhead environments
- Ask whether the plan stays entirely in open water. A wreck or cave listing is not permission or training to enter.
Historical access notes exist for this record, but have not been independently verified for current use. Request current directions from the operator or site manager rather than following an old entry description.
Questions, answered
Is The Castle (Bicheno) suitable for my certification?
The record lists Deep/Advanced + experience. That does not establish suitability for every route or day. Share your training, recent experience and equipment needs with the operator and ask about the specific proposed dive.
Can I book The Castle (Bicheno) through YouDive?
YouDive is an independent research directory. Contact an operator directly to confirm whether it currently runs the trip, the inclusions and the booking terms.
What you might see
Southern rock lobster, bullseyes, cardinalfish, banded morwong, long-snouted boarfish, butterfly perch, bastard trumpeter, rock cod, abalone, sea whips, yellow zoanthids, jewel anemones, small gorgonians, yellow sea spiders
Location
Two large granite boulders and a 30 m tunnel on the eastern side of Governor Island, about 20 m off the island, Governor Island Marine Reserve.
Before you make plans
Conditions, access and operator schedules can change. This is a location guide, not a dive plan. Ask a local operator about current conditions and suitability for your training and experience.
Sources & further reading
michaelmcfadyenscuba.infoccwtasmania.commarinelife.org.auparks.tas.gov.auindopacificimages.comRecord updated 27 Sept 2026. Source claims are being reviewed.