Bordeaux
"You cannot drink Cabernet and Merlot without tasting what they taste like from their homeland, Bordeaux (well, you absolutely can, but this is more fun)." Bordeaux creates some of the most mind-bending examples of Cabernet Sauvignon and Merlot, with a strong earthy quality. The region is quite large, so even though the most expensive wines in the world can be found here, there are also tons of great values (source: European Wine Exploration Map _ Wine Folly.pdf).
Bordeaux is well off this trip's Champagne–Alsace–Burgundy axis, but it completes France's "big four" reds alongside Burgundy (Bourgogne), the Rhône Valley (Rhône Blends) and Beaujolais. Wine Folly's starter guide ("The First 4 Wines You Must Try From Bordeaux") suggests tasting the four major styles to get going (source: European Wine Exploration Map _ Wine Folly.pdf).