What is the importance of the coal mine in the novel, The Industry of Souls?

The coal mine, about six kilometers away from the prison camp, is where Shurik spends the bulk of his time. It is nicknamed the "mole hole." Early in the mornings, before dawn, the prisoners are driven there by truck to begin their long days digging for coal. The mine is two kilometers beneath the earth's surface. There, the prisoners are given short pick axes; and the work entails hacking away at the walls of the mine. One day Shurik's group encounters a unit of women prisoners. They are described as being somewhat sexless; thin, with short hair, wearing loose clothing. The mine has taken away not only individual freedoms, but identities as well. Shurik has sex with one of them. As he does, they talk of a beautiful landscape somewhere with a church, where snow is gently falling. Their moment of pleasure brings them into another world, if only for a short time.