After solving the Knocked Out Stairs Puzzle
, explore the main area. Some Dragur will come out of the coffins and attack you, including a stronger Draugr Deathlord. Some cultists will join in on the fight too. Once you have neutralized all the enemies, go down the stairs. Continue down the corridor and activate the handle to open the door. There will be some Draugr in the next room, including Restless Draugr and Draugr Scourge, so be ready for combat. There are some urns to loot in this chamber and a shelf with healing potions.
Continue through the halls, watching for traps as there are many in this area, including swinging log traps and spiked barrier traps. Watch for pressure plates on the ground, which are tiles that have a glyph mark on them, such as this one:
After passing the spiked wall barrier trap, you will arrive at a fork, with the left path branching downwards and the right path going up. Go right at this fork. Soon you arrive at a big wooden door, but watch out for the flame trap. Past the door, there is a big hallway with pendulum traps. Frea says she will wait until you deactivate them. Time your movement carefully through the swinging pendulum blades, going forward one section at a time. It is recommended you save frequently during this stage (but don't rely on quicksave so that you are not left with a hopeless save if you accidentally save right as a trap kills you). Watch the swinging blades and run past each portion when the time is right. Once you get to the end of the hall, pull the lever to open the door in front of you as well as to deactivate the swinging blade traps so that Frea can join you.
Go straight, then turn left and open the iron door to enter another big area. There will be a locked gate on your right with a drawbridge behind it. To your left, there is a window of a small room with a handle seen inside. Go straight through the open entry in the wall and turn left, arrive at the small room and activate the handle. Go back to the Drawbridge, which will lower once you approach it. Go down and into a large chamber where you will be attacked by more cultists and draugr.
Cross to the far end of the room, and enter the Temple of Miraak Sanctum.