Couly-Dutheil is the largest of the long-established Chinon producers, run by the same family since 1921 and based in cellars cut into the tufa hill below the fortress. They farm vineyards across the appellation and are widely sold abroad — likely the Chinon you have already drunk if you have drunk Chinon outside France.
The cellars open for tastings most days of the week, with two or three different cuvées poured and a guided walk through the limestone tunnels where the wine is aged. Their Clos de l'Echo and Clos de l'Olive are the best to ask for. Reserve ahead in summer; smaller producers in the surrounding villages offer more intimate visits if you have a car.