One of the reasons we chose this cruise was due to the amount of time spent on land! We were not enthused about the idea spending multiple days in a row at sea (although I will admit we ended up enjoying our time on board way more than we expected to!). The trip only has two sea days and they are spread out early in the trip and one on the last day before you get back to Copenhagen. The rest of the days are spent from around 8AM until 4PM out in the cities and then each evening you get back on the boat and travel at night to your next port.
As far the the sea, I found it to be quite calm. I have never been on a cruise before, so I don't have a reference point, but mostly very smooth sailing. Obviously everything is weather contingent, and we did have one night with some rain and wind, and you could feel the boat swaying a bit, but overall a smooth and easy trip. Hope this was helpful!