I have no clue where I can find this dungeon,the quest guide just tells me to enter and burn Cassandra's body, but that's it. I've been stuck on this quest for a few hours now, trying to find it.

For the love of Bracchus Rex, help me.

Bumpaaaaa

It's under the temple of the dead in the Phantom Forest. You need to telport in by placing a pyramid on that circle with the lever at the temple of the dead.

Any idea where the temple of death is in phantom forest ? I can not find it...

Ruined structure with a bunch of those invincible sentinel statues. In the middle there's a teleport platform with a lever.

I found it But now I can't seem find the secret wall, my perception is really high (15) and using the potion boosts it up to 18, yet I still can't seem to find it.

Usually I don't have a lot of issues with quests, but this one is really yanking my chain.

Found it - problem solved.