What is the key village of the Baden wine region?

The key village of the Baden wine region is indeed Kaiserstuhl-Tuniberg. This area is renowned for its production of high-quality wines, particularly those made from Pinot varieties such as Pinot Noir, Pinot Blanc, and Pinot Gris. The unique climate and terroir of the Kaiserstuhl region, which features volcanic soil and a warm climate, contribute significantly to the expression and character of the wines produced here. The region also benefits from a long history of viticulture and boasts a diverse range of winemaking styles.

In contrast, the other options relate to different wine regions in Germany or beyond. Würzburg is a significant town in the Franconia region known for its white wines, particularly Silvaner. Pfalz, another prominent wine region, is known for a variety of white and red wines but is not part of Baden. Mittelrhein is a smaller wine region recognized for its steep vineyards along the Rhine River, emphasizing Riesling, yet again does not pertain to Baden. Therefore, Kaiserstuhl-Tuniberg is specifically recognized as the key village within Baden, making it the correct answer.