It’s a quick TGV to get to either Reims or Epernay. Hard to do both in one day but either one gives you a nice glimpse of the champagne mystique. Reims is a bigger city with several nice cathedrals and the museum of the surrender which is very interesting if you can squeeze it in. Epernay is smaller, cleaner and has a couple of well known champagne houses. I like both. When I’m in Reims, I usually visit Veuve Clicquot and when in Epernay, I liked the visit at Moet & Chandon but the train ride through the caves of Mercier was pretty great too.