Three prisoners spent the night on a roof at Mountjoy Prison after climbing up last night.
Prison authorities have launched an investigation after the men managed to get out of their cell block yesterday evening.
A total of four prisoners attempted to climb onto the roof of a low building inside the prison walls.
One man got stuck on the way up and was taken back into custody yesterday evening by prison officers.
But three of the men spent the night on the roof before being persuaded to come down.
It's understood the effort to get onto the roof was a protest action.
All four men are now back in secure detention.
