ksmambho-’nalanila-viyan-mana-indriyartha-

 bhutadibhih parivrtam pratisañjihirsuh

avyakrtam visati yarhi guna-trayatma

 kalam parakhyam anubhuya parah svayambhuh

 

Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 

 

After experiencing the inhabitable time of the three modes of material nature, known as two parardhas, Lord Brahma closes the material universe, which is covered by layers of earth, water, air, fire, ether, mind, ego, etc., and goes back to Godhead.

 

Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 

 

The word avyakrtam is very significant in this verse. The same meaning is stated in Bhagavad-gita, in the word sanatana. This material world is vyakrta, or subject to changes, and it finally dissolves. But after the dissolution of this material world, the manifestation of the spiritual world, the sanatana-dhama, remains. That spiritual sky is called avyakrta, that which does not change, and there the Supreme Personality of Godhead resides. When, after ruling over the material universe under the influence of the time element, Lord Brahma desires to dissolve it and enter into the kingdom of God, others then enter with him.