What are the best day trips from Paris?

Giverny is the one. If you take a single day trip together, make it this, and that's not a soft recommendation. Monet's house and gardens at Fondation Claude Monet run April through October, and the water lily pond looks exactly like the paintings, down to the Japanese bridge and the willows trailing in the water. Take the 8:15 Intercités from Gare Saint-Lazare to Vernon (50 minutes, roughly €15–30 return depending on when you book), then the shuttle bus from Vernon station; it's timed to the train, €10 round trip. Get there when gates open at 9:30 and you'll have about 45 minutes before the tour groups arrive. The smell of wisteria in May is so thick it's almost physical. Lunch at the Hôtel Baudy in Giverny village: the Impressionists gathered here when visiting Monet, and the garden terrace seats fill by noon, so put your name down early.

Reims is the champagne day, and it works better than Épernay for couples because the city itself has things to do between cellar visits. TGV from Gare de l'Est, 45 minutes, €15–50 return on Ouigo or regular SNCF. Book a morning tasting at Taittinger: their chalk cellars are 4th-century Gallo-Roman quarries carved into the hillside, cool and damp year-round, and the tour is interesting even if you're not a wine person. The cathedral is a ten-minute walk from the cellars: the Chagall windows throw blue and red light across the stone floor on clear mornings. Worth noting: the light only really works before noon, so don't save the cathedral for last. For lunch, Café du Palais on Place Myron-Herrick still has its 1930s Art Deco interior and the croque-monsieur is better than it has any right to be at that price point. You'll be back at Gare de l'Est by 6 PM with time to change for dinner.

Versailles is the obvious answer. If neither of you has been, go, but go with realistic expectations. The palace interior on a Saturday in July is shoulder-to-shoulder, and you will spend more time in queue than in the Hall of Mirrors. The gardens are the real draw for two people: 800 hectares, the Petit Trianon where Marie Antoinette played at farm life, and the Grand Canal where you can rent a rowboat for about €15 per half hour. RER C from central Paris, 40 minutes, roughly €7.50 return. If one of you has already done Versailles, redirect to Chantilly instead: 25 minutes by train from Gare du Nord, about €17 return, and the Domaine de Chantilly holds the second-largest old master painting collection in France after the Louvre, with maybe a tenth of the crowds. The grounds were designed by Le Nôtre, same landscape architect as Versailles, and the cream at the Hameau is the best Chantilly cream you'll eat anywhere. Which makes sense, given the name.

For the split-interest flex day: Chartres if the history buff picks, Auvers-sur-Oise if the art lover picks. Chartres is one hour from Montparnasse, €16–32 return, and the cathedral's stained glass dates to the 1200s: the blue they used is a specific cobalt that nobody has fully replicated since. The old town slopes down to the Eure river and has restaurants that feel like they haven't changed menus since the 1990s, which in this case is a compliment. Auvers-sur-Oise is 35 km north, about an hour by train via Pontoise, where Van Gogh spent his last 70 days: the wheat field he painted behind the church is still there, and the room where he died at the Auberge Ravoux is open for visits. Small, quiet, done by 3 PM. Dinner back in Paris.