Warning: Minor Spoilers Ahead!
After completing the Scoundrelâ€™s Folly, Snow Veil Sanctum will be marked on your map (you can travel their by heading North-East from Windhelm, or South-East from Winterhold). Mercer will be waiting for you just outside the entrance; be sure to speak with him before attempting to enter the cairn to learn vital information about the former leader of the Thieves Guild and his untimely demise, and murderer Karliah. Once you’ve learned all that you can from Mercer, hop down into the circular depression and to trigger Mercer’s opening of the door to the catacombs.
Inside you find much resistance throughout the dungeon as Karliah has reset all the traps that she disabled on her way in, she was also skilled enough to not wake many of the draugr as well. These traps include but are not limited to tripwires, beartraps, hanging oil lamp traps, swinging spike walls, just be cautious throughout this dungeon. When you arrive in the first room with all the coffins, make sure that you position yourself behind the swinging spiked wall before pulling the chain to open the gate to the next area to avoid being hit.
Once you make it through the crypt area you will arrive in a section that has a raised platform with two coffins on it. Make sure to take the wooden stairs to the South of this room first as it will lead to a Larceny Target sitting on a pressure plated pedestal that activates a hanging oil trap.
Note: it is recommended that you attempt to clear the area of all loot, then grab the Larceny Target and run off the ledge to the North. We attempted to set off the trap before looting and the explosion caused the Larceny Target to fly resulting in a fifteen minute search of the surrounding area before locating it under a draugr body on the lower level.
Now head up the stone steps in the room once you drop down and continue to trek through the dungeon, going through a door leading to the Snow Veil Sanctum. Delve deeper into the sanctum until you reach a room with an iron gate; that low humming you hear is a word of power along the Southern wall of this room. Keep pushing on until you reach the nordic puzzle doors, and watch Mercer-Frey magically open the door without the use of a claw.
Step through the door and witness an epic twist that completely changes your outlook on Mercer-Frey as you learn the truth behind what really happened between Karliah, Mercer-Frey, and Gallus (the previous guild leader) on that faithful day. At the end of the events you will have in our possession, Gallus’ journal written in an foreign language, a target who may be able to translate it, a new ally, and a new foe. Speak with your new ally for additional information to complete Speaking with Silence, and to begin the quest Hard Answers.