Fibula is a small island and town south-west of Thais. To come from Thais to Fibula you must cross a tunnel (here).
The people on Fibula rely mainly on Fishing, Farming, and Hunting wildlife to make a living. Locked deep below the surface are many dangerous creatures in the infamous Fibula Dungeon. Just north of Fibula is another island called Calcanea that used to be inhabited by humans, but one day a Giant Spider came to the surface and killed them all. Everyone who lives on Fibula fears the same thing may happen to them one day. There have also been reports of a great sea monster in the bay just north of Fibula.
In the real world a Fibula is a bone in the leg.