Great Barrier Reef and Ningaloo Reef - a general overview of the scuba diving:

GREAT BARRIER REEF

Coendozn's review of the Great Barrier Reef is pretty close I think. Perhaps he (or she) hasn't been brutal enough in saying that if you are an advanced diver, don't go on a trip to the inshore reefs, and particularly don't go on a scuba diving trip that is still teaching students. The further out reefs, and more expensive tips, are the ones to go on.

NINGALOO REEF

Ningaloo Reef (on the other side of Australia - the west side) also has some great great diving. You can dive out of Exmouth, or out Coral Bay, which is about 150km south of Exmouth. Ningaloo is about equivalent to the outer reefs of the Great Barrier Reef. It is more wind dependent, but all reefs are close to shore and are done as day trips. Not lots of night life, but enough. Good onshore facilities and good dive operators.

The Elbow at Coral Bay is amazing sometimes. Pretty often really amazing. Big animals, sometimes bigger than you might prefer. I had dives there on consecutive days with amazing mantas barrel rolling so close that you could have touched them sometimes.

The whale sharks are a seasonal thing, and it is just snorkeling. It can be expensive but worth it as a one off. Whale shark season is about March to maybe June or July, it can vary.

Exmouth has more sites than Coral Bay and more options if the wind is from the west. It also has some good hiking in the ranges nearby. It is not quite like Colorado, but you wouldn't have come to Australia for Colorado scenery. On that subject, the land based activities in the Cairns and Port Douglas areas are excellent, and much better than in the west.

A trip combining Exmouth and Coral Bay would be a very good trip.

Coral Bay and Exmouth get seriously hot in our summer (Dec, Jan, Feb). Think in terms of hotter than Texas in summer.