Reef HQ is the education center for the Great Barrier Reef Marine Park Authority's headquarters and is the largest living coral reef aquarium in the world. The highlight is walking through a 20m-long (66-ft.) transparent acrylic tunnel, gazing into a giant predator tank where sharks cruise silently. A replica of the wreck of the SS Yongala provides an eerie backdrop for blacktip and whitetip reef sharks, leopard sharks, and nurse sharks, sharing their 750,000-liter (195,000-gal.) home with stingrays, giant trevally, and a green turtle. Watching them feed is quite a spectacle. The tunnel also reveals the 2.5-million-liter (650,000-gal.) coral-reef exhibit, with its hard and soft corals providing a home for thousands of fish, giant clams, sea cucumbers, sea stars, and other creatures. During the scuba show, the divers speak to you over an intercom while they swim with the sharks and feed the fish. Other highlights include a touch tank and a wild sea-turtle rehabilitation center, plus interactive activities for children. Reef HQ is an easy walk from the city center.