Thank you everyone for your wonderful suggestions! It has made me even more excited to go on our trip (finally booked the flights today - yay!).
CCole187 - All of your suggestions look great (had a bit of a Google session!) - Skyview looks especially amazing, so I think that will be going on our *must do* list. Might have to have a mooch around the ABBA museum to - just to say we were there!
Mediana - Nothing specific that I am interested in, just like to see as much of a city as possible while there... Although, DH does like architecture and historic buildings (as do I) so it would be nice to find something in that respect (eg. St Peter's in Rome, Notre Dame in Paris etc.) I do try my best to eat local foods when I am visiting somewhere, so a nice restaurant with proper Swedish food would be on my list.
JJ91 - Sundbergs Konditori sounds like one of the first places I am going to have to visit! I can't think of anything nicer than a nice cake after a few hours wandering round...
I was thinking of going to the Ice Bar as well, just for the experience - I know you have to book for this in advance - is it worth it??
Thanks again
PP xx