There is a community aspect, which is balanced well with the solitary aspect; St. Bruno was inspired with these ideas by the Holy Spirit. They have liturgy and go for a 4 hour hike so they get to know each other better and get some physical exercise. They speak to each other twice a week.
The Carthusian can be a cloistered monk or a brother, two different ways of living the same vocation of solitude. The solitude is not lived for its own sake, but as a privileged means of attaining intimacy with God, it is a calling from God (vocation).
The Carthusian day revolves around the liturgy, a group of meditations, chants, hymns, readings and prayers put together in such a way that make them relevant to the time of day and time of year, they are in union with God. First they have ‘Prime’, 3 hours later is ‘Terce’, then at the sixth hour is ‘sext’, ‘none’ at ninth. The evening hour is called ‘Vespers’, and the night hour called ‘compline’, then ‘matins’, the early morning hour of long readings. After this is the dawn hour, ‘lauds’, an acclamation of praise to God for the new day, then back to ‘prime’ and over again. These can be influenced by culture, climate and sunrise/sunset, they revolve around the mass.
Everything is done in solitude except matins, lauds, mass and vespers, which are celebrated in the church and on major feast days and Sundays, are all said in Church. They have their heads shaved every 2 weeks and are allowed beards (no moustache) except the fathers. Family can visit once a year for 3 days.
I think the Carthusian life is so extreme because of the way their life is so solitary and dedicated to God. They are far more focused on God than any other contemplative order.
I think it is a hard and harsh life to live, but they do it to get closer to God, the solitude is not lived for its own sake, but is a privileged means of attaining intimacy with God. They are called by God to do this; this is why it is a vocation. It is a journey towards the heart and all the value of our life is shaped towards this goal. They help the monk unite his life to charity, introducing it to the depths of his heart.