Mystery Theme '72 by FrankensteinP

Question 12

The snow-covered Stockholm neighborhood seen in the foreground of the attached link is named after a near-by bit of civil engineering; an archaic English word for the same bit of civil engineering is the theme of this quiz. Either the theme, the civil engineering structure, or the name of the Stockholm neighborhood pictured will be accepted.

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Watergate (or Lock) (or Slussen)