These holes are not only amazing, but some of them are really
terrifying - especially #8!  The sheer scale of these holes
reminds you of just how tiny you are. 
  

1. Kimberley Big Hole - South Africa 
  

Apparently the largest ever hand-dug excavation
in the world, this 1097 meter deep mine yielded 
over 3 tons of diamonds before being closed in 1914. 
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2. Glory Hole - Monticello Dam, California A glory hole is used when a dam is at full capacity and water needs to be drained from the reservoir  This is the 'Glory Hole' at Monticello dam, and it's the largest in the world of this type of spillway, its size enabling it to consume 14,400 cubic feet of water every second.

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3. Bingham Canyon Mine, Utah 
  

This is supposedly the largest man-made excavation
on earth.  Extraction began in 1863 and still
continues today, the pit increasing in size
constantly.  In its current state the hole is
miles deep and 2.5 miles wide. 
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4. Great Blue Hole , Belize  This incredible geographical phenomenon known as a blue hole is situated 60 miles off the mainland of Belize.  There are numerous blue holes around the world, but none as stunning as this one.

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5. Mirny Diamond Mine , Serbia 
  

This one is an absolute beast and holds the title
of largest open diamond mine in the world.  At 525
meters deep, with a top diameter of 1200 meters,
there's even a no-fly zone above the hole due to
a few helicopters having been sucked in. 
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6. Diavik Mine , Canada The mine is so huge and the area so remote that it has its own airport with a runway large enough to accommodate a Boeing 737.  It looks equally cool when the surrounding water is frozen.

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7. Sinkhole in Guatemala 
  

These photos are of a sinkhole that occurred early
this year in Guatemala.  The hole swallowed dozen
homes and killed at least 3 people. 

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8. And the most terrifying one of all This is the famous 'Rat Hole' that you have heard about.  It is capable of swallowing trillions and trillions of U.S. Dollars... Annually!  Including a current $700 billion bail-out!

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(I didn't see that coming..... Did You?)