Maintenon

Train from Paris Montparnasse on the line to Chartres.

The exquisite Château de Maintenon, which once belonged to Louis XIV's second wife, who became known as Madame de Maintenon. A "bite-sized" chateau for those who don't want to spend a day walking round visiting a vast edifice.
It's a bit of a hike into town from the railway station (although there are occasional local buses) and the chateau is not an "A-list" site so there is no tourist industry built around it. However, there are enough bars and restaurants in town to satisfy all but the most demanding traveller.
Pay to go into the Chateau. It has the most fabulous, really spectacular portrait gallery, including paintings of the family from recent times. Unlike the big chateaux, this one is small enough to enjoy without getting bogged down with 'too much information'. The written guide is useful but there really is so much to look at and inspect. The history of the place is fascinating, (given this is a very small town) and the gardens are fabulous too. From the courtyard the small, formal lawned gardens take you to the lakes....and beyond the lake is the fantastic aqueduct, used to take water to Versailles palace.

From the chateau, it's an easy drive to Nogent le Roi, another small town with an impressive array of medieval buildings, a chateau, small public park and magnificent church. This one, with the sun shining through its glorious windows, is an inspiring place to visit.