The cellar was built at least 40m below the ground, giving a cool temperature for aging champagne. There are about 2 million bottles in this cellar where they have another cellar far away with over 20 million bottles.
Some of the bottles are doing remuage. The cellar was built by first making a well of a few meter deep, then excavate down to 60 meter. It has to be in pyramid shape for structural safety.