Reims and Eparnay are both conveniently located in the Champagne region, about 130 km east of Paris. You can take a high-speed train from Paris to Reims, which takes about 45 minutes and will cost around €20 one-way. To travel between Reims and Eparnay, local buses are available, do check their schedules as they might not be frequent.
If you have more time, consider visiting the Champagne-Ardenne Regional Nature Park for an outdoor adventure. You can spend your time hiking, cycling and horse-riding through the rolling hills and vineyards. On the other hand, tourists with less time can skip some of the champagne houses and museums, but you shouldn't skip the Palace of Tau as it houses many treasures from the cathedral.
You can fly into Charles de Gaulle Airport (CDG) which is approximately 148km from Reims or Orly Airport (ORY) which is slightly further away at approximately 160km from the city. From there, you can take a train directly to Reims city centre.