This monastery was nearly unique in its organization,* with the religious living the solitary lives of hermits within an enclosed community. They lived alone in their cells, only coming together once a day for Mass and eating one communal meal on Sundays. Other than this, they lived, ate, and worked alone in their cells. Anything they needed from outside reached them not through the door, but through a small revolving compartment or a horizontal shaft with a bend in the middle so that they never saw the person outside. Any necessary contact with the outside world was delegated to lay brothers.
[Plan of the Carthusian monastery at Clermont, found in: Viollet-le-Duc, Eugène, Dictionary of French Architecture from 11th to 16th Century, 1865. Source: Wikimedia Commons]
[Monastery of La Grande Chartreuse, photographed 2006 by Floriel, source: Wikimedia Commons]
*There were other hermit orders but not very many and this is the best-known.
**From the 18th century onward.
Barber, Malcolm. The Two Cities: Medieval Europe 1050-1320. London: Routledge, 1993.
Cook, William R. and Ronald B. Herzman. The Medieval Worldview: an Introduction. New York: Oxford University Press, 2004.
Hill, Bennett D. "Carthusians." In Dictionary of the Middle Ages, edited by Joseph R. Strayer, 118-120. New York: Charles Scribner's Sons, 1983.
Lawrence, C. H. Medieval Monasticism. London: Longman, 1984.
The Carthusian Order - The Order's official site
Carthusians - Wikipedia