Some favourites in the Rendsburg area of the NOK (Use of car may be beneficial at 2 & 4)
North bank facing south :-
1) Hotel ConventGarden Terrace if you buy a beer or coffee every few hours
2) The Bruckenterrassen Cafe under the High level rail bridge; good for lunch and drinks as above. There is a guy here who announces the ships (in German only) and plays their national anthems.
South bank (better in good weather due to sun position):-
3) South end of foot tunnel from adjacent to Hotel ConventGarten as above
4) Kanal Cafe in Osterronnfeld Am Kamp-Kanal (Excellent place to stay, very reasonable and really good food especially cakes!!!) 2 bedrooms overlook the canal
When closed, I use the car park if poor weather