It might sound like a weird idea, but the Paris metro is worth at least one date. There are lots of interesting stations to look at (check out the stairs in the metro Abbesses -- a beautiful mural covers the entire wall). The line 14 is new and futuristic. Lines 6, 5 and 2 are sometimes above ground. Every line is different and as you go from one end of Paris to the other you may not see buildings or streets but you certainly will see lots of people, and it's amazing how just that is enough to tell where you are. Try taking a line as far from where you live as possible and get out to walk around and discover a new neighborhood. You will always find something new in Paris, no matter how long you've been here. It's one of the beauties of the city.