1) Strait of Finland 
Kvarken (Swedish Kvarken or Norra Kvarken (as opposed to South Kvarken), Finnish Merenkurkku) is the narrow region in the Gulf of Bothnia separating the Bothnian Bay (the inner part of the gulf) from the Bothnian Sea. The distance from Swedish mainland to Finnish mainland is around 80 km while the distance between the outmost islands is only 25 km...