Entrance through MacGuffin CastleEdit
On the second floor of MacGuffin Castle, there is a prison cell with a manhole that gives access to this area. Once in the cave, you follow a path to the different areas and find different rewards: resource crates, golz and gems.
In one of these cave areas, there is a secret that will give access to more loot.
As you progress through the main quest, you will be able to return to this area and find a dragon. Defeating the dragon will allow you to get an important artifact: Saint Drake's Blood (which unlocks the MP regeneration item power "Dragon's Blood").