Tunnels are dug by engineers, who assemble at the pit of the tunnel and start digging when a target area is selected. The tunnel crumbles upon reaching the target, dealing massive damage to buildings in its vicinity. Engineers can be seen taking trips between the start and the end during digging.
Up to six workers can participate, which hastens the digging process, by adding them through the tunnel's panel. An Engineer's Guild must be present in order to assign workers.
The entrance of the tunnel takes up a large area and it is vulnerable to attacks while digging is commencing. Unlike in previous games, the engineers cannot be attacked through the opening.