Besides various AIS apps, the deck on a ferry is a good place for spotting the obvious photo location. If you are very near the coast, the coast is very near the shipping lane you are sailing in right now! The Møns Klint, the Danish variant of The White Cliffs of Dover, is such location.
The cliffs rise nearly 130 meters above the sea and is an impressive landmark to watch when you are travelling on the ro/pax ferries between Malmö and Trelleborg in Sweden to Travemünde and Rostock in Germany.
It was on a crossing on one of these routes, I some years ago made the above conclusion; and realized that I needed to make a dedicated photo trip to the beach on the foot of Møns Klint. Since then I have been in the area three times. First direct in front of the cliffs, then on the beach a little further south and the last time on the shore just below the Møn Lighthouse.
Despite I have been there three times with my camera I haven’t got any photos of the scenery itself, so if you not familiar with the site you can check it out here: wikipedia.org