These tunnels have been inhabited by monsters for several hundred years, and it doesn't seem like they will be cleared out for practical use anytime soon. This location has five areas. The first two are non-missable, you have to visit them during the story. The other three are missable. You can access the Operations Area No. 5 after leaving the mines during the story. The Large-Scale Mining Zone and the Excavation Area become available via the quest At Hatred's End (on disk 1) or by talking to the Seasoned Adventurer in Athlum's pub (on disk 2).