The environment created by Unlimited Void is a literal empty void of space that appears to take the target to the center of the universe itself.
The Unlimited Void presents the target with limitless information, forcing them to see and feel everything while seeing and feeling nothing at the exact same time. This phenomenon paralyzes the target with infinite knowledge, causing them to die slowly. Only the caster and anyone they are physically touching are free from the void's effects. The Unlimited Void is also an extremely polished Domain, as it was able to easily suppress Jogo's Coffin of the Iron Mountain Domain.  While cursed spirits can last within the domain for a while, humans would not last long. Just 0.2 seconds within the Domain would take about 2 months of rehabilitation for any normal person once they're free.
Gojo expanded his Domain the first time against Jogo to counter his Domain. There, Jogo is forced to process all the information presented to him by the universe at once, paralyzing his mind and body infinitely. Before Jogo perishes, Satoru closed his domain and took his opponent's head off.
Gojo later activated his Domain against Jogo, Hanami, Mahito, and Choso, limiting it to just 0.2 seconds to avoid inflicting long lasting damage to the civilians caught in his domain. He then executed all the Transfigured Humans in the giant crowd of his immobile victims.