This quest is part of the Wyrm Hunt quests Ser Maximillian gives you. Select the option to "Investigate a Cult" to start this quest.
Learn more about Salvation
Talk to Mason
Renew your inquiry into Salvation.
Search the catacombs
Observe the gathering
Defeat the undead
Pursue Elysion
Report your findings
Talk to a man named Meredith inside the Gran Soren Union Inn. Next, find Mason in the slums and talk to him as well to obtain the Salvation’s Badge. This will mark the cult members among the populace which you can talk to and update your quest. After speaking with them, the location of the catacombs will be marked on your map.
Travel to the catacombs due west of Gransys. Just stick to the roads if you don’t want to get lost. Otherwise, just follow the marker and you’ll reach it eventually. There’s also a riftstone outside where you can use to replenish your pawn’s HP or re-arrange your party. The catacombs are pretty much straightforward so light up your lantern and start exploring.
There are lots of undead in the area so have your fire-spells and enchantments ready. You can also start opening the stone caskets to find either good loot inside or reanimated corpses. Continue until you reach a door with a lever. Pull the lever to unblock the path then proceed further inside. You’ll eventually reach a lift. Operate the lever nearby to ride the lift down to the lower floor.
Follow the hallway and you’ll reach a locked gate. Ignore it for now but do remember it later on since it’s part of a quest. Continue to the left and make it to the next hall. Find the door with a lever then pull it to open the next path. Proceed forth and follow the path until you reach a chasm with some wooden walkways. If you take the opposite side of the wooden walkway past the ladder, it leads you to a deadend (be careful of the two skeleton warriors inside) with a chest. Now follow your path and cross the narrow bridge leading to another cavern.
In this cavern lies two chests and an ogre. Defeat it and enter the next hall. With the circle of the marked meeting place nearby, you can continue to the southeast and remove the barricade from the door to enable an alternate route to the Catacombs. This exit is called Rear Passage and will bring you back a short distance south of Gran Soren.
Head to the meeting place and observe the cult congregation to trigger a scene. After the scene, you have to clear the room of fresh undead. Exit the room to trigger another quest. Here, a short sidequest will trigger (Justice Done) where you have to decide whether to kill the cult leader or just leave him. Either choice will complete the sidequest. Exit the catacombs and talk to Maximillian to get your rewards.