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A view of the interior staircase of the cylindrical tower. In the center of the image the cylindrical exterior wall is visible and on the left side of the image the massive solid interior column.
Note how the staircase is bonded to both the exterior wall and the interior column. The woman in the image is about 5 ft. 2 in. [1.3 m.] tall.
There actually is an outer “cylinder” (right side of image) that is constructed around a round central column (left side of image) and stairs are wedged in between the two parts.