This was once a place of great power. The highborne who lived here would host lavish parties, living in splendor.
Zin-Azshari was once on the shores of the Well of Eternity and drew powerful mages from all over the empire to study here. I suspect, despite the many years at the bottom of the sea, there are still treasures and powerful artifacts hidden away here.
Speak with the spirits that remain and see what you can find. There must be something to help us overcome the Guardian of the Tidestone.