We'll have 3 days available between departing Luxembourg and arriving in Paris on the morning of day 4 to catch the Eurostar. We've visited Paris a few times, so I'm looking for suggestions about where to visit during our 3 available days that will be accessible by train. We'll be traveling at the end of December, so hiking is likely not realistic. Ideally, we would prefer to base ourselves somewhere and day trip rather than bounce around, but if it's worthwhile, we could stay in a couple of locations.
We enjoy exploring interesting corners in old towns, museums, and unique local sites. We usually walk all day and then hang out in the town center for some people-watching, although it may be too cold. Less interested in cathedrals, WW1 sites, or touring champagne cellars.
Suggestions??