Were the Earth hollow, it might be difficult to control the buoyancy of the hot air balloon sufficiently to enter a hollow Earth at the poles.
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Agartha
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a valley
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Botches
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Many theorists believe that the entrance to the Earth hollow is
located at 87.7 degrees North latitude and at 87.7 degrees South
latitude which is the location of the North and South Pole. These
polar openings lead directly to the Earth's core which has led
these theorists to believe that the Earth's hollow is in the center
of the Earth's core.