I know you did not ask for things to do (your husband may have that all planned) but my suggestions would be:
Walk up to 2nd level of Eiffel Tower. The queues for the lifts can be quite long and you can walk up one of the legs to the second level. It is not too bad a walk and the views are amazing.
Go to the Monmatre area and the Sacre Coeur (church). This is where the Moulain Rouge is (if you have seen the film). It is slightly out of the centre but is a small "village" in it own right with narrow lanes and grape vines. More great views as it is on a hill.
Go on a boat trip up the seine, called Bateaux Mouches. See here
http://www.bateaux-mouches.fr/
Try to go early evening as the buildings are flood lit and it is is very romantic.