There are several great options for 2-day side trips from Paris that are easily accessible by train. Here are a few suggestions:

1. Versailles: Just a short train ride from Paris, Versailles is known for its stunning Palace of Versailles, a UNESCO World Heritage site. Explore the opulent palace, its beautiful gardens, and the Trianon palaces. It’s a perfect day trip to experience the grandeur of French history and architecture.
2. Giverny: Visit the charming village of Giverny, located about an hour from Paris by train. This is where the famous painter Claude Monet lived, and you can explore his house and gardens, which inspired many of his famous works, particularly the water lily series.
3. Chartres: Known for its magnificent Gothic cathedral, Chartres is a medieval town that offers a rich cultural and historical experience. The Chartres Cathedral is a UNESCO World Heritage site and features stunning stained glass windows.
4. Reims: Located in the Champagne region, Reims is known for its prestigious Champagne houses and its grand cathedral. Take a guided tour of a Champagne cellar, explore the city’s historic center, and visit the magnificent Reims Cathedral.
5. Honfleur: Situated on the Normandy coast, Honfleur is a picturesque harbor town known for its charming narrow streets, colorful buildings, and art galleries. Take a stroll along the Vieux Bassin (Old Harbor), visit the Sainte-Catherine Church, and enjoy fresh seafood at one of the many restaurants.
6. Loire Valley: If you’re interested in castles and wine, consider a trip to the Loire Valley. Take a train to Tours and explore the region’s stunning châteaux, such as Château de Chambord and Château de Chenonceau. You can also visit vineyards and taste the renowned wines of the Loire Valley.

These are just a few options, and there are many more beautiful destinations near Paris that you can explore within a 2-day trip. Make sure to check train schedules and plan your itinerary in advance to make the most of your time.