Behind the swinging door on the right (west) side is a small area with two pillars with pull chains on the other side and a spiked trap on the side. To open the last door in the last room, both pull chains must be activated. Behind this door on the right another chain closes the just opened door.
How to get final descent quest in Skyrim?
This quest takes place in Raven Rock Mine. Enter the mine and follow the corridor. Inside are two figures having a heated argument in the first room of the mine, Crescius Caerillius and his wife Aphia Velothi. Talk to Aphia first, then to Crescius.
How do I enter the Ashfallow Citadel?
Ashfallow Citadel is a former Imperial stronghold northwest of the Stone of the Sun in eastern Solstheim. Inside the tower, in the basement, a stone door cannot be opened at first until the Served Cold quest begins. The inner parts of the citadel are defended by the assassins of Morag Tong (×8) and the Severin family.