Mercier is near Moët et Chandon, and you can visit them both on the same day. Mercier conducts tours in English of its 18km (11 miles) of tunnels from laser-guided trains—reached by an elevator that descends past rudimentary champagne-themed dioramas. The caves contain one of the world’s largest wooden barrels, with a capacity of more than 200,000 bottles. No reservation is necessary if there are fewer than 10 in your group, though you may want to call ahead for the schedule of English tours.