Grenen

Known as "The Branch" in English, Grenen is a slowly lengthening strip of beach that marks the intersection of two seas which are continually forcing more sand to the surface. 

Skagen is the northernmost town in Denmark, and at the top of the town is the northernmost point in Denmark, Grenen. This is where Kattegat (the waters between Denmark and Sweden) and the Skagerrak Straight (part of the North Sea) meet. The clash of the two massive bodies of water make the area very treacherous to swim in due to powerful and unpredictable currents. However, it is one of the few places in the world where visitors can put one foot in one sea and one in the another.

Due to the constant movement of the waters, the sandy strip of land is continually (if slowly) being extended as the tides push more sand to the surface. Given enough time, it is possible that the two bodies of water will no longer be connected but instead, Denmark and Sweden will have a new land bridge.