Which fortress that controlled the entranceway between Kattegat and Øresund was in "Hamlet"?
Kärnan:  It is the only part remaining of a larger Danish fortress which, along with the fortress Kronborg on the opposite of Øresund, controlled the entranceway between Kattegat and Øresund and further south the Baltic Sea. Kronborg:  Immortalized as Elsinore in William Shakespeare's play "Hamlet", Kronborg is one of the most important Renaissance castles in Northern Europe and has been added to UNESCO's World Heritage Sites list (2000).
Kronborg