If you take a look at a map you will see that Rotterdam is not directly located at sea. To reach the cruise terminal of Rotterdam your ship needs to sail up the New Waterway which will take +/- 3 hours. During this time you will sailing through the largest port of Europe with here and there your typical Dutch landscape. The structure you see on the picture is the Maeslandkering. This is one of the largest moving structures on earth designed to keep the lands of the Dutch dry.
New Waterway, Rotterdam