During our visit of Bhaktapur we met Mr. Pushpa Lama (master painter since 1983) from the Unique Thanka Production Centre. It’s office is near Dattatraya Square and he is saling many very nice Mandala.
Kalachakra mandala is at first designed by the 6th dalai lama,this lineage transfered up to present dalai lama also.it is considerd as a device that shows a path way from life to the nirvana. Based on the ancient tibetian ideology it tells you the method to reach to the nirvana.It is considered as a meditational device. It also represents the cosmos system which consists of the five major elements of life. Namely – Fire , Earth , Water , Air and Space
Depending of your mind (peaceful and cleared mind, meditative, graceful or dark mind) then you will not use the same door.
and after this there are 14 different rooms in the castle representing 14 different steps to reach t nirvana.
and when you complete all the different steps then you reach to the center to nirvana.

Kalachakra Thangka Mandala