A day trip to Epernay

Epernay is about 1 hour and 15 minutes by train from Paris. Have never been to Dom Perignon, but the Mercier (68 Avenue de Champagne) tour is entertaining. There are a number of good restaurants in Epernay -- one to consider is Le Cepages. Epernay can be done in a day trip; arrive at around 10 AM and do one tour followed by lunch and an afternoon tour and catch a train at around 5:30 back to Paris. Unlike Reims, with the historic cathedral, to me the draw in Epernay is the champagne houses.

Dom Perignon is made at Moet Chandon. I think I remember that there's a large statue of Dom in front. Moet Chandon does tours by appointment only. You might want to have your hotel in Paris call the day before and set it up for you. I didn't tour Moet Chandon, as I had not made a reservation, but I agree that Mercier is quiet enjoyable (no reservation needed). Lots of good restaurants in town.

I visited Moët&Chandon in 2006 and liked the tour. There is also a lot of history linked to this brand what made the tour interesting. Have no idea if something has changed, but at the end you can taste a glas of champagne and buy some bottles in all kind of sizes, from quart/piccolo (0,2L) up to Nebukadnezar (15L) if I remember well.
You can also buy there the exclusive Dom Perignon from different years for exorbitant prices, first see the pricetag before believing it, some over €1000,-!
Moët&Chandon is some 15minute walk from the Épernay railwaystation, much closer then Mercier.

Luckily, that is a regional train, departing Paris Est station, so you don't have to worry about the higher price and reservation rules of the French TGV trains. You can buy 2nd-class tickets at the station for about 24 euros each way, per person.

Thanks everyone, just the information we needed!

Very easy to do by train. Perrier Jouet is also on the avenue of Champagnes in Epernay. I have been to the region twice but have not taken the Moet and Chandon tour, so cannot comment. I would definitely do more than one tour as some are better than others and they all do not include the same content. Epernay would be an excellent place for lunch. I would make a full day with a late morning tour, lunch, and an afternoon tour before going back to Paris.

I did Epernay as a day trip last year from Paris. You can book the Moet tour online - they run tours in single languages, so you want one of the English tours. We were able to get from Paris to Epernay in time for the 11 am tour - in fact we had time to stop at one of the other smaller champagne houses as well as the tourist office before the Moet and Chandon tour. (Do stop at the tourist office for a good map). We walked from the train station to the tourist office which is on the main street where you will find many of the houses.

We had a nice lunch in town. We then took a tour run by one of the small family run businesses. The owner picked us up in Epernay in her van, drove us to her vineyard, took us around the area a bit, and then we had tastings in the family cellar. Very informal and a good way to see some of the outskirts of town and the vines. (The champagne was very good and very inexpensive). She then drove us back to town in time to catch our train. The name of the winery is "Champagne Domi Moreau" - you can google them and see the details of the tour.

This was a really nice day and a good balance of the very large and the very small.

Haven't done Epernay, but did a guided tour of Reims with parischampagnetours.com. They picked us up from our flat in Paris, breakfast served in the van, tour of the vineyards, tour of a small champagne house - Champagne Cuperly (amazing), then a phenomenal lunch, tour of the cathedral, then to Pommery and a tour of their chalk caves, and back to Paris in time for dinner. All for $200/pp. I'm pretty sure they have walking tours as well. Good luck, and enjoy your trip!