I was an exchange student in Australia in 1983 and had the good fortune to be able to spend two days diving the Barrier Reef. Memories I'll never forget -- was able to grab onto the shoulders of a manta ray with a 15' wingspan and glide along a few feet above the ocean floor for hundreds of feet. Colors and variety to rival the best dive spots in the world. Urchins galore. Truly a mesmerizing experience.
Here's someone else's video of the experience: