SS Yongala Queensland, Australia When the SS Yongala left Melbourne in March 1911, its captain, William Knight, was probably thinking not of the voyage at hand, but the following one, which would be its 100th trip in Australian waters. As it turned out, that milestone trip would never be taken; three days after setting to sea, Yongala sank in a Pacific cyclone, taking 122 souls with her to a 95-foot grave. It sat, undisturbed, until located by sonar nearly half a century later. Its name on the bow, a safe in the purser's (identified by the manufacturer as having been delivered to the Yongala) and the ship's bell all confirmed the identity. Exactly what sank it, though, still remains a mystery. All that's known is that it steamed into the storm and never steamed out. Today, the 350-foot, English-built, passenger-and-freight steamer is Australia's most-famous shipwreck and one of the best dives in the world. The wreck is located entirely within the boundaries of the Great Barrier Reef Marine Park, and its depth (42 feet to its top and 95 feet to the bottom) is deep enough to protect it from most wave action. The Yongala seems to have become home to nearly all the 1,850 marine species associated with the Great Barrier Reef. Groupers and turtles abound, and rays sweep by, along with thick sea snakes and even guitarfish. Heavily encrusted with growth, Yongala also has become a thriving ecosystem worth multiple dives. Quick Guide: Yongala Dive (yongaladive.com.au), a PADI IRRA Dive Resort, is the only Ayr-based dive center. Their fast boats cover the distance in just 30 minutes. Mike Ball Dive Expeditions (mikeball.com) and Spirit of Freedom (spiritoffreedom.com.au) offer luxury live-aboard adventures, which include the Yongala. Check out Trip-n-Tour (trip-n-tour.com) for a selection of dive travel-package options.