How Would You Spend 24 Hours in Paris?

You all have been so helpful so far planning my European trip (I can't believe we leave in two weeks!) and now I have a new challenge for you. My good friends Mark and Diana will be in Paris while I'm in London and I've decided to take that chummy old Chunnel to visit them for 24 hours before continuing on to meet Craig in Munich. This begs the question: WHAT TO DO IN PARIS FOR 24 HOURS? Or, more importantly, WHAT TO EAT IN PARIS FOR 24 HOURS? Don't forget, I've been there once before, so this trip it would be nice to try some new things (though returning to Pierre Herme is definitely on my agenda). Also, looking for a dinner spot that's super special but not insanely pricey (current thoughts: Restaurant Le Chateaubriand or Frenchie). Have at it, smart people! Merci beaucoup.