As far as I know there's only one Supermax prison in the United States and that Supermax Prison is the ADX Florence Supermax Prison which is located in Florence Colorado.
In that prison inmates spend 23 hours per day locked in their cells and an hour outside in a rec cage.
The prison cells in the ADX Florence Prison have the showers in the cells as well so the prisoner doesn't need to leave their cells to shower.
They also have their food brought to them and slid through a slot in the door.
The ADX Florence Prison has been said to be worse than death.
Once you go in you don't see much daylight until you leave that prison.