It's in fact isn't a mission (it doesn't appear in your journal) but an interesting addition - at the same time it's interesting and quite complicated. In order to experience it, you will have to obtain at least two Kagrumez Resonance Gems. Below are their locations:
- one can be bought from Revus Sarvani, who has set a camp northwest of Tel Mithryn;
- one can be found in the ruins of Fahlbtharz (in the mountains east of the Water Stone);
- one has been hidden in Nchardak (inside the room in the northeast - you have to jump there).
After obtaining at least two stones, head to the ruins of Kagrumez - you will find it to the south of the Temple of Miraak. Take the elevator down and deal with three Bandits who inhabit the underground. By their leader you will find more Gems. As you should already have four, you will be able to solve the below puzzle.
If you place two stones like shown above, you will be surrounded by a metal cage. When your "cell" opens, you will be attacked by a whole bunch of Dwemer machines - you need to destroy them. Once the rooms is filled with scrap-metal, head into the corridor on the left - it's a Dwemer forge (inside you can find lots of useful blacksmith tools).
If you pull the lever in the middle of the room, you will open a stash with a friendly mechanical spider. At this point the real mission will also activate - Find Resonance Gems across Solstheim to complete the Kagrumez Trials.
Find Resonance Gems across Solstheim to complete the Kagrumez Trials
Arrange the resonance gems as shown in the above screenshot. You will be once again locked in a cage (this time a bigger one) and the room will be filled with flames and an army of machines. In order to break free, you need to defeat all the enemies - only then the trap will turn off and you will be able to move on.
Enter the forge in which you came across the friendly Spider. You will surely notice that the door which was locked before is now open. Head through it and enjoy the treasures. Afterwards pull the level and meet with another friendly machine - this time a sphere. Greet it and return to the main room to solve the puzzle.
Set the stones as seen above and you will once again (this time for the last time) fall into a trap. The room will be flooded by poisonous water and a few more machines - spiders, spheres and ballistas. Deal with the close range enemies as fast as possible and afterwards move to those who use ranged attacks (be sure not to fall into the water!). Once you take care of them, head through the forge to the last room.
Beside the destroyed centurion you will find lots of treasures and valuables and beside the platform by the furnace - a mediocre bow. If you turn left, you will enter a room with a chair - apparently Kagrumez was once used as a coliseum - all the chairs face the arena on which you just fought.