Part of the wall is visible in this photo of the Foxden Mine.
The Great Wall of Foxden is a 4km-long wall which completely encircles the Kingdom of Foxden, protecting it from the Wilderness beyond. There is only one entrance/exit to the Wilderness from the wall.
The wall has never been fully breached, and has only come close once before, on 21 January 2014 following a mining accident. Following this event, it was discovered that the top half of the entire wall is made of silverfish blocks, launching fears of a silverfish epidemic in the future.