The Great tunnel was an ancient dwarf tunnel running down the Ered Luin. In Forlindon it remained an active trade route, leading to a road to Mithlond (the Grey Havens). Travellers could take the ferry across there, and then a path to the White Towers. At that point the route connected to the East road. In Harlindon, the tunnel was largely ruined. The Great Tunnel was masterpiece of dwarf engineering & magic. Dwarf-Light provided a dim light for the whole route. The main tunnel was normally safe, but side passages could lead many places you shouldn't go. The dwarves patrolled the Great Tunnel.