A tunnel is used for escaping, getting around the prison secretly, and storing contraband items. It will need to be supported by a timber brace when it gets too large and can be lit by a candle or a flashlight.
If the guards shake your cell down and the tunnel isn't concealed by a desk, it will be filled in, making you lose any candles, timber braces or items in it.
Tunneling is one of the most effective ways to get yourself out of a prison. Tunneling is also used as your second storage to hide your contraband items from the guards. You will need to use a Shovel or a Trowel to dig your way under the ground. But you need to use pickaxe to dig through concrete floors or rocks. If you do dig a concrete floor using shovel or trowel, you will only get soil but no hole (The Escapists 1 only, you can dig through paved floors with shovels in TE2). If you want to dig a large tunnel, you will need some Timber Braces to support the structure from collapsing. You can lighten up your tunnel by putting some Candles in your tunnel.
If you want to dig a tunnel outside, you must do it at night if you don't want to get shot by the snipers (even if you wear a Guard Outfit). You can cover the hole by using soil (or dirt) on it. This will repair the hole by a certain amount of durability, but the tile will still be damaged (and you will have to dig it again to enter the tunnel.) You can also place a Desk over a hole to hide it. This is very important if you don't want the guards or snipers to find the hole and bust you. If the guards did find the hole, you will be sent to solitary and your progress on your tunnel will be reset to zero. All the items in your tunnel will also vanish.