Siren's Tower

Dalnakya Cavern is a location in Final Fantasy Brave Exvius. Located at one of Grandshelt Isles (and thus, a part of the Kingdom of Grandshelt's established territory), it is home to the esper Siren.

Story
Long ago, Siren was sealed away in the Tower due to its fearsome power. However, the eventual breaking of the Earth Crystal by Veritas of the Dark weakened the seal upon it and allowed Siren to break free once more.

Two knights of Grandshelt who witnessed the crystal's shattering, Rain and Lasswell, journey to Siren's tower in hopes of receiving help from the esper so they can become stronger. Upon completing her trial, they are bestowed with her power, and are also given a request that they restore light to the world.

Bewitcher's Trial
It unlocks when Siren reaches level 30.