Chateau les Crayeres - including a meal at their divine restaurant - in Reims
Le Bouclier d'Or in Strasbourg (not luxury, but we enjoyed it)
Le Chambard, a R&C in Kaysersberg (Alsace)
Hostellerie La Cheneaudiere, a R&C Spa hotel a bit W from Alsace, if you're looking for some R&R to break it up.