R on a boat, going on a hour-long cruise in the Curonian Lagoon.
There are many boat cruises out of the Nida harbor. Some are as short as an hour: they sail along the Curonian Spit up to the border with Russia, say hello to the Lithuanian coast guard ship patrolling the border, turn around and go back. Others are 4-5 hours long: they cross the Curonian Lagoon and visit interesting coastal towns on the continental side. Unfortunately, there is no way to find out in advance if a particular cruise that interests you will be sailing on a given day, because they only sail if they get enough customers. On the day we were in Nida, we were able to get on an hour-long cruise to the Russian border and back. It gives you a view of the biggest dunes of the Curonian Spit. A pre-recorded narrative tells you about the places you see in three languages -- Lithuanian, Russian and German. (There are lots of German vacationers in Nida.)