Like the Moon Temple and Stargazer's Tower, the Sun Fort was built before the Middle Ages (c. S.700). It served as a fortress during the countless wars between Erebonia and Calvard over the territory now known as Crossbell.
Its enormous bell was removed during an investigation in S.1185, which can now be seen at the center of Crossbell City.
After authorities destroyed the D∴G cult in S.1198, the survivors found new shelter in the Sun Fort. They found the laboratory once established by the Crossbellan alchemists and put its high-tech facilities to use. This is where Joachim Guenter completes his work on Gnosis.
The Special Support Section, accompanied by the Bright siblings, descend deep into the Fortress. In the depths, they discovered the missing citizens and the captive mafia who were kidnapped by the cult.
Eventually the party finds and confronts Joachim Guenter, and manages to end his reign of cruelty after Renne provides some assistance.
Lloyd's group tracks Ilya Platiere and KeA Bannings here but are ambushed by Heiyue and Garcia Rossi after San San betrays them due to the curse. They defeat Heiyue and the former Revache boss but almost fall to a surprise attack by the twilight dancer who turns out to have been Ilya. They manage to escape after the battle when Zeit saves them.