The three-year retreat is the practice of remaining in strict meditation retreat for three years and three fortnights. The most favorable conditions for retreat can be found in a secluded place, with limited contact with other people. The benefits of such a meditative retreat are enormous.
According to the Vajrayana teachings, three years and one and a half month ( lo sum chok sum, three years plus three halves of 30 day lunar cycle) is the minimal period necessary to purify all winds of the subtle energies in our body and to transform them into primordial wisdom winds.
This timeframe is to transform karmic energy into wisdom energy. It was derived from the teachings of Kalachakra Tantra.
It is said that generally, in the course of a day, we breathe in and out some 21,600 times. And every thirty-two times there is the arising of what is called the 'wisdom wind'. This means that in a single day the wisdom wind arises 675 times. If we consider the life expectancy of a human being to be roughly 100 years, then in one lifetime we experience the wisdom wind for a total of three years and three fifteen day periods.
"All the wisdom energy which circulates during one hundred years equals three years and three fortnights. When all karmic energy is transformed into wisdom energy, enlightenment is attained. This is the reason why it is said that the state of the Buddha Vajradhara is achieved by meditating for three years and three fortnights."
In the Kagyu tradition, the title 'lama' is given to those who completed at least one three-year meditative retreat.
In three years, the best retreater fully accomplish the practice; the average one attains qualities, such as the signs of heat, and the lowest on without error, takes hold of the beginning of the path leading to liberation and omniscience. In this way, retreat is endowed with many special benefits.
It is a tough practice and we lay people should show our deep respect and reverence to the fortunate Lam who has undergone such retreat.
Please refer the Schedule of Practice in the Special Six Yogas of Naropa Three Year Retreat Center attached as image and appreciate the series of activities carried out during the retreat.
I have posted this to give awareness on the tough retreat. We layman can't practice it, however we should support those who undergo such extreme retreat of long isolation.