How about a Canal boat ride? You can get a boat from Camden Lock to Little Venice, past Regents Park & the zoo & they tell you some interesting history about the area.
As you're staying in Swiss Cottage, get the bus up to Hampstead and go for a walk on the heath, very romantic! And check out some of the historic pubs around there. My favourites are the Holly Bush in Holly Bush Vale and the Spaniards Inn where John Keats reputedly wrote Ode to a Nightingale, it has a lovely garden right next to the Heath.
Also get yourself a copy of Time Out and see what's going on.