Behind the giants' castle

After sneaked into the giants' castle, the team found out an gigantic structure right behind it, it not just generates heat, smoke and unbelievable noises, but also seems to draw out the energy from the mother ground...
Across the sea was the holy island of the north man, but right now has been occupied by a huge floating "thing", the team start to feel that the "thing" could be the cause of all troubles...