Lights of Arlathan

The Lights of Arlathan are magical elven devices, a sort of lanterns required for the scrying necessary to locate the Eluvian in Witch Hunt. They are located in the Cadash Thaig where the refugees from Arlathan were sheltered before the thaig was destroyed by the army of Kal-Sharok.

Upon entering the thaig, Finn initiates a dialogue in which he reveals that the Lights are magically hidden from sight for everyone except the inheritors of their original masters, such as Ariane. In order to locate the Lights, he needs a vial of her blood as a spell component.

As you proceed further in the thaig, follow a trail of magic vortices that mark the way to the Lights. Place a party member in the vortex and watch for moving lights. If you are standing in the right vortex, the lights will move in one direction and disappear at the same spot where the Light of Arlathan is hidden. Have Finn cast the spell using the Blood of Elvenkind to make the Light visible. After you pick the Light, Ancient Elven Guardians (either two bosses or one elite boss, of various specialisations) appear to defend it. There are four Lights to collect altogether.