Planning first trip

Hi there, we are planning our first trip in May. We are there for 10 nights total. We love to walk cities, eat great food, and enjoy local culture. We move pretty quick so we tend to spread these out to a few cities. We have so far 3 nights in Paris, 3 nights in Bordeaux. We want 1 night back in Paris but we have 3 nights to fill. We won't have a car so we are relying on trains. Cannes and Monte Carlo would be cool but look very far away. Any idea for any 1) closer adorable beach towns or 2) other vibrant cities closer to Paris or Bordeaux? Thank you!