At this moment Noah is taken to a place called an underground prison. From outside it's just a one story building. But inside it is a completely different story.
After entering Noah was thrown to a cell on the first floor, there is no second floor above the first floor. All the floors in this building are built underground, that's how it got its name underground prison.
After the elders put Noah in a cell on the first floor they left without any worries as if they believed Noah won't be able to run away even if he wants to. After all Noah's Cultivation is sealed right now or that's what they have thought.
However, Before leaving the prison one of the elders talked with the prison guard about Noah and told them to Give special care to Noah, and this special care is nothing much but letting him see Those who come to see him.