Denmark’s northernmost point, Grenen, hosts a unique natural phenomenon. Here, two seas meet, namely the Skagerrak and the Kattegat; and the collision of the waves is clearly visible to the naked eye. This fascinating tourist attraction, Grenen, is a spit formation consisting of deposited sand and gravel carried along by the strong currents; and over the last 100 years, this barrier has increased its length by 1 km. As the large beach expanse at the tip of Grenen is constantly moving, there are frequent occurrences of lagoons – attracting both playful children and adults, as well as wading birds.

Credits:  https://www.visitnordjylland.com/  
  

The Dune of Råbjerg Mile is the largest migrating dune in Denmark. The westcoast has for many centuries struggled with migrating dunes due to the harsh wind and sand covered areas - and being close to Grenen in Skagen, the weather at Råbjerg Mile is far from mild. 
Each year the dune moves around 15 meters towards Northeast, closer to Grenen, the top of Denmark. Attempts of afforestation did not stop the migrating dune, which is expected to cover the main road to Skagen in a century or two. Once the dune reaches an area trees, or other plantation, it takes approximately 40 years for the tree to re-emerge on the other side of the dune, which covers an area of roughly 1.000 square meters and reaches a height of 20 meters.  

One of the best attractions in the neighbourhood of Skagen (Dk). Also visit the Grenen location early in the morning. In the day it is quite crowded. 

(Credits: www.visitnordjylland.com )