Off Hornby Island you can dive to a spot where you can (apparently) sometimes see six-gill sharks. This (to me) is interesting because it's apparently the only spot where they're found in water as shallow as that and it's the only spot in the world where they come into non-tropical waters or something like that.
Sam, I looked at the Contiki site, it looks like the learn-to-dive trip will be the Great Barrier Reef? That's probably worth it. Last time I made it down to GBR was 2001 and I
can't wait to go again. Truly magnificent stuff. Only drawback to GBR is that you have to boat it out to the reef, along most places of the shoreline it's solidly offshore (e.g., an hour's boat ride) (there are parts where the reef touches the coastline but those places are closely guarded secrets, plus very inaccessible and treacherous accesses usually). As opposed to some good dive destinations (Cozumel, Fiji, Carribean) where you can walk offshore and see reef. But the reef is probaby one of the most amazing sites you'll see in a lifetime, so it's
totally worth it. Man, I hope I can go back there soon. (Sigh.......
)