Blue Hole (Castalia)
The Blue Hole captured the public’s interest because of its size, about in diameter, clarity, vibrant blue hue, and enigmatic "bottomless" appearance. Contrary to prevalent belief, the depth of the Blue Hole is not unknown, but has been sounded and found to be about deep. Water temperature is about throughout the year. Floods and droughts have no effect on temperature or water level. The Blue Hole is fed by a passing underground stream which discharges of water daily into Sandusky Bay to the north, feeding into Lake Erie. The water contains lime, soda, magnesia and iron, and because the Blue Hole is anoxic, it cannot naturally sustain fish. The surrounding terrain is developed on limestone bedrock and exhibits karst topography due to dissolution of the limestone by ground water, creating water-filled sinkholes. The Blue Hole was known to American Indians and was first recorded in history in 1761. Several similar blue holes are known to local residents. The Blue Hole that once was a tourist attraction is now off limits to the public. It is located on the grounds of Castalia Trout Club. It is to be distinguished from another hole similar in size and eerie bluish-green color. This latter hole is owned by the Castalia State Fish Hatchery operated by the Ohio Department of Natural Resources, Division of Wildlife and is open for public viewing.
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".)