Complex sentence: The two best known mines in the area are Lockgrufvan, which dates back to the Middle Ages, and Storgruvan, also called Moon Mine due to it being the home of the test moonbase analogue test project.
Split into simpler sentences: The two best known mines in the area are Lockgrufvan, which dates back to the Middle Ages, and Storgruvan. Storgruvan is also called Moon Mine due to it being the site of the moonbase analogue test project.