Great Blue Hole
The Great Blue Hole is a giant marine sinkhole off the coast of Belize. It lies near the center of Lighthouse Reef, a small atoll from the mainland and Belize City. The hole is circular in shape, across and deep. It was formed during several episodes of quaternary glaciation when sea levels were much lower. Analysis of stalactites found in the Great Blue Hole shows that formation took place 153,000; 66,000; 60,000; and 15,000 years ago. As the ocean began to rise again, the cave was flooded. The Great Blue Hole is a part of the larger Belize Barrier Reef Reserve System, a World Heritage Site of the United Nations Educational, Scientific and Cultural Organization (UNESCO).
Macarthur, New South Wales
Mushroom Tunnel is located just off the Remembrance Driveway (Old Hume Highway) heading towards Tahmoor and was built in 1867. It is considered one of the earliest pre-Federation railway tunnels in New South Wales. In 1919 the 65 metre long tunnel fell into disuse when a new railway deviation was built. The tunnel then served as a mushroom farm and ammunition storage facility during the war years. Currently the tunnel is empty although it is popular with ghost-hunters due to many local folk tales claiming that it is haunted. Subsequently it has been featured by both print and television media.Thirlmere Lakes National Park is part of the Blue Mountains Heritage Area in which the park consists of 5 important freshwaters lakes that are abundant in waterbirds and native reeds. The lakes are among the last undisturbed lakes within the proximity of Sydney and are believed to have high ecosystem-related and environmental scientific value. ("For more information, see Thirlmere Lakes National Park".)