what does "turn tightly around"mean?
They climbed the stairs to the second floor. The staircase turned so tightly around the lift shaft that it was a succession of blind corners. The door to Flat 2 was identical to that of Flat 1, except that it was standing ajar. They could hear the growl of Lechsinka’s vacuum cleaner from inside.

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Answer

It means that they couldn't see around the corners at each turn of the staircase because it turned so abruptly and sharply. In a wide spiral staircase it curves gradually and you can see ahead of you. On this staircase the turns were sharp and you couldn't see around the corners.