Srila Prabhupada – “These material universes are created by the dreams of Maha-Visnu" (Purport SB, 4, 29 Text 83)

Maha Visnu is the Supreme Lord (Visnu-tattva expansion of Krsna) and is seen in painting simultaneously sleeping and dreaming.

And this entire material creation of individual Brahmanda universes ARE His dreams.

This is why in all paintings of Maha Visnu, He is seen sleeping and dreaming.

Srila Prabhupada – “This material creation is the spirit soul’s dream. Actually all existence in the material world is a dream of Maha-Visnu, as the Brahma-Samhita describes–

“This material world is created by the dreaming of Maha-Visnu. The real, factual platform is the spiritual world, but when the spirit soul wants to imitate the Supreme Personality of Godhead, he is put into this dreamland of material creation”. (Srimad Bhagavatam Canto 4 Chapter 29 Text 83)

Srila Prabhupada - “Everything happening within time, which consists of past, present and future, is merely a dream. This is the secret in understanding in all the Vedic literature.” (Srimad Bhagavatam Canto 4 Chapter 29 Text 2b)

Srila Prabhupada - "Factually all of material existence is only a dream. Thus there is no question of past, present or future. Persons who are addicted to karma-kanda-vicara, which means ‘working for future happiness through fruitive activities’, are also dreaming. Similarly, past happiness and present happiness are merely dreams" (Srimad Bhagavatam Canto 4 Chapter 29 Text 2b)

The entire material creation is the dreams of the sleeping Maha Visnu.

Deep inside each massive Brahmanda universe coming from Maha Visnu, is a secondary universe where Maha Visnu expands as Garbhodakashayi Visnu.

From Garbhodakasayi Visnu, who is found deep inside each Brahmanda, a Lord Brahma appears on the top of a lotus flower that grows from Garbhodakasayi Visnu's Navel.

Deep within each Brahmanda, inside a secondary universe, Lord Brahma then builds (creates) the many Planetary Systems within each of their inner secondary material universe.

There is only one Maha Visnu in the entire material creation (1/4 of the Spiritual Sky) however, there are billions of Garbhodakashayi Visnus and Lord Brahmas because there are billions of Brahmanda universes, each with their own secondary material universe within them.

All the Garbhodakashayi Visnus and Lord Brahmas are within their own secondary universe, that is surrounded and encased by this outer Brahmanda greater universe.

As said above, all these massive Brahmanda universes originates from Maha Visnu's breathing and the pores of His skin.  

And all activity going on deep in each Brahmanda, including all material bodily vessels, all originate from the "dreams" of Maha Visnu.