Walls are the basic unit of structure in a prison. They disallow players to pass into another area, and act as a good divider.
Destruction
Walls can be destroyed by using chipping tools (i.e., crowbar, flimsy shovel, sturdy shovel). Keep in mind that some special walls(ones that are covered in decorations or designs) are indestructible.
Dangers
If the guards spot a broken wall, they will raise the Security Level. If they see you breaking a wall, then a lockdown will trigger and you will be sent to solitary. This can be avoided by replacing the wall block after you have finished using your passage, or by crafting a fake wall block as a removable replacement. A better alternative for the Fake Wall Block is the poster, an item with infinite durability that can cover up wall damage.