How do I get out of the prison?

[Jargonaut]

I break out of the jail cell and open every locked gate. However, when I got to the stairs, it says "The prison sentence is guarded. You need to find another way out".

I have search all the walls for hidden buttons, but have not found any. How am I suppose to get out of the prison?

Thanks

[Elendil / Redshift]

All prisons have a way out. For example you can escape the prison of Matras through a drain. Other prisons have other exits.