What Lurks Below - NWN Side Quest (Chapter 2)
What Lurks Below is a side quest that begins by speaking with Jax outside of the Archaeologist Barracks on the East Road map. Jax will also give you the Archaeologist Barracks Key when you accept this quest which is needed to access the barracks next to him. Inside the barracks you'll find additional side quests so I strongly recommend you go in.
For this quest you'll have to enter the nearby Troll Caves and work your way down to the 3rd floor. Every one of the cave entrances on this map will go into the Troll Caves so it doesn't matter which you pick. While exploring the caves make sure to complete The Simpleton's Mother and A Troll Head Trophy quests, as stated before they both take place inside these caves.
You'll find the entrance to the Creator Ruins on Troll Caves - Level 3. How these ruins work is on each level you'll find a Seal Guardian Golem (pictured below) that will prevent passage until you complete the task it asks you to. On the first level you need to find a Ring and bring it to the golem and on the 2nd level you'll have to acquire a password.
While you're on the 1st level of these Creator Ruins you'll also want to grab the Prism Blossom Seed that you can find in a crate. This item is used in Boddyknock's Tale which is his Henchman quest for this Chapter. You'll find this item near the first Seal Guardian Golem, for the exact location check the Boddyknock's Tale quest entry.
Below is a more information about each of the Seal Guardian Golems and how to get past them.
Level 1 Guardian Golem: Obtain the Ring of Gax in the southeastern portion of this area and bring it to the Seal Guardian Golem. If you need to see the map location of this ring use my screenshot above.
Level 2 Guardian Golem: For this Guardian Golem you'll have to obtain a Creator Scroll which is found in a chest at the 4 way intersection in the south. This scroll will say "Thurth mog lama gat rag" which is the password you'll need to say to the Golem to proceed to the next floor.
Level 3 Guardian Golem: This Seal Guardian Golem will attack you the moment it sees you. Defeating it won't unlock the door, you'll still have to find the body of a Dead Thief and loot the Stolen Seal Key to unlock the door leading to the final part of the ruins. You can find the Dead Thief's body to the south of the Seal Guardian Golem, it's in the central most room on the map. Hold down TAB to locate the corpse, it'll be named 'Dead Thief'.
On the final level of the Creator Ruins just before the Portal that will lead you back to the surface you'll find a treasure chest with "Complete History of the Creator Ruins" inside of it (pictured below). This is the only item you need to complete this quest so make damn sure you grab it otherwise you're going to have to make a long trip back down.
With the Complete History of the Creator Ruins Book in hand all that's left is to return to Jax and turn in this quest.