MMORPG.com Wizard 101 Correspondent Matt Plourde writes this guide for the Sunken City Dungeon.
After defeating Lord Nightshade, you will discover a place called Nightside. The door to Nightside is hidden behind the waterfall near the Rainbow Bridge in the Wizard City Commons. Apparently, the Death School fell into a ravine! Here, you can learn the remaining Death School spells and some taunt/de-taunt spells as well. Further, the entrance to the Sunken City is in Nightside. Marla Stinger needs to prove that Grubb exists, and you are tasked to help her.
Read the Sunken City Dungeon Guide