Originally, this was a quest that involved one of the discovered Soul Crystals that imprisoned Bael'Zharon. Unlike with the Fenmalain Vestibule, Caulnalain was secured by the Shadow forces. However, the Shadows failed to protect the crystal from Isparian attack and it was destroyed. On its corpse were Soul Gems that were used to create unique crystal items. It has since been replaced with a weaker replica that drops less powerful gems.
Route: Run from Neydisa Castle or take the Windrune Cottages portal from Crater Lake at 66.4N 14.3E.
Once you portal in, jump down into the area below using either the east or west room, it doesn't matter which.
At the bottom go into the south west room and head down the passage, once you reach the T section head left and then take the second left turn heading south.
You will come to a room with green lighting in two corners, take the east passage from this room and just follow the path all the way to the room with the Caulnalain Gate. You will find that the gate is just metres away from the pit you dropped into at the start.
The last part is very easy to navigate as the only way to progress is by jumping down a pit at the end of each section. After the second jump head east into the area with the Caulnalain Crystal.
Once you have defeated the crystal loot a gem and take it to one of the brothers in Uziz (24.4S, 28.7E) for your reward.
You give Gersan the Sureshot Caulnalain Gem.
Gersan the Sureshot tells you, "A rare and powerful gem. Here is your bow, infused with the crystal's essence. Remember that this bow can only fire ammunition made from crystal fragments, which I can make for you if you give me crystal shards. I am sure you appreciate how rare the gems are, so take care not to lose your bow!"
Gersan the Sureshot tells you, "If you desire a crossbow, you must attach it to a stock yourself. If you desire an atlatl, give me back the bow and I'll see what I can do."
Gersan the Sureshot gives you Caulnalain Crystal Bow.
You've earned 2,045,377 experience.
Gersan the Sureshot tells you, "I've also taken the liberty of granting you some practical knowledge..."
The Vestibule dungeons were revised during A Small Victory with higher level creatures and a new level restriction. The Caulnalain Shield and Orb was also updated.