|Location||Under Lazulis Castle|
It was half-dug by the Reptids and then flooded by the sea. It connect various of the caves that run under the Island. It runs from the Castle Depths to the sea and back to the Reptid's Cave. It is Chapter 25's setting, when the Count sent a party of knights to investigate it and the mercenaries go searching for them after they go missing.
It is crowded by Sea Reptids. The Kraken resides here.
When repeating the area, you can farm Sylph Bowstrings in a gold chest after the first battle. Also, in the area where you would find Dagran and Syrenne originally, there will be a large group of Reptids and Cave Cougars waiting. If you defeat them, you have the possibility to find a Blade +5 in one of the many gold chests.