#5 Dean's Blue Hole.
Long Island has many wonderful attractions, but Dean's Blue Hole is the most unique. Dean's Blue Hole is the world's deepest known salt water blue hole with an entrance below the sea level. It is in a bay west of Clarence Town on Long Island, Bahamas.
Besides being the world's deepest known ocean blue hole with 660 feet deep, it happens to be absolutely gorgeous. Deans is very safe to dive, but children and non-swimmers should stay well away. The drop-off from the sandy beach into Deans is extremely sudden.
#4 Mount Baldy - Sand dune.
Mount Baldy is a sand dune located in the Indiana. It is on the southern shore of Lake Michigan and is 11 feet deep. It is a wandering dune that moves or shifts every year, so it is called a "living dune."
In 2011, unexpected sinkholes, began appearing in the sand, and a boy actually got stuck in one, It took many hours for the boy to be rescued from the 11-foot pit. He was luckily saved after.
#3 Ice Cube Neutrino Observatory Hole.
The IceCube Neutrino Observatory is the first detector of its kind, designed to observe the neutrinos from deep within the South Pole ice.
This giant telescope was built in the ice of the Antarctic plateau at the South Pole. The final stretch of construction ended with the drilling of the last of 86 holes.
It was built using heated pipes and each hole is 1.5 miles deep.
#2 Great Blue Hole.
The Great Blue Hole is a large underwater sinkhole off the coast of Belize. It is a world-class destination for recreational scuba divers attracted by the opportunity to dive in crystal-clear waters and see myriad species of marine life.
The hole is circular in shape, over 300 metres across and 125 metres deep. The world's largest natural formation of its kind. It became famous after Jacques Cousteau said it was one of the top scuba diving locations in the world.
#1 Monticello Dam Morning Glory Spillway.
Technically known as the Morning Glory Spillway but it is locally known as "The Glory Hole." It is located in northern California, the Monticello Dam's is the largest morning glory spillway all over the world.
This funnel-shaped outlet, allows water to bypass the dam when it reaches capacity, as it swallows a rate of 48,400 cubic feet per second. Not a safe place to swim.
