The Elder Scrolls IV: Oblivion Remastered lets you embark on a familiar yet nostalgic adventure through Cyrodiil. While speaking to Kud-Ei, you will hear about her missing friend, and about how she requires your help. This will start the Through a Nightmare, Darkly side quest, and this guide will explain how to complete it in Oblivion Remastered.
Through a Nightmare, Darkly Side Quest Guide Oblivion Remastered

To start the side quest, head over to Bravil’s Mages Guild and speak to an NPC called Kud-Ei. Ask her about Henantier and she will tell you about how she misses her friend since he left to perform experiments against the wishes of the Guild. She will also tell you that she wants to reach out to him, but he is apparently trapped within his experiment.
Accept her request to help her out, after which you will be led to Henantier’s House. Once inside the house, you will notice a sleeping Henantier, but Kud-Ei will tell you that it is part of his experiment. He is now trapped within his dreams and unable to get out. Also, ask her about the Dreamworld Amulet, which can help you gain access to his dreams. She will warn you that if Henantier dies in the dreamworld, you and he will die in real life as well.
Henantier’s Dreamworld
Get the Amulet from Kud-Ei, equip it, then fall asleep on the bed next to him to access Henantier’s dreams. You will appear without any of your inventory items, but don’t worry about it. Collect whatever you can find within the room you spawned in, then speak to Henantier. Also, you can’t use your spells inside the Dreamworld either, which is something to keep in mind.

Next, look around to find four doors that will lead you to different puzzles. There are two doors on the upper floor and two on the lower floor. There is no particular order to start the puzzles, so choose any floor and any door to try your luck. Below are the ways to solve the Test of Resolve, Perception, Courage & Patience.
Test of Resolve

For this test, you need to fight two minotaurs inside an arena. You can use your bare fists for the fight or pick up the weapons at the entrance of the arena to make the fight easier. Set your game difficulty to low if they are proving too much of a bother. Once done, a set of stairs will appear leading up, and on the upper platform you can pick up the Element of Resolve. You will be teleported back to Henantier, and you can hand over this item to him to complete one part of the quest.
Test of Perception
This test can be a bit more difficult, as you need to traverse a room filled with traps. Your best bet here is to just make a run for it and keep following the floating red crystals. Take care not to fall over the ledge, as it is instant doom for you. If you notice pressure plates on the floor, jump over them to not trigger them.

Take your time while crossing the area filled with swinging blades, and watch out overhead for larger blades that might fall on you when you cross under them. Just keep running to avoid the traps. You will eventually reach the area where you can pick up the Element of Perception, take it and head back to Henantier.
Test of Courage
Once you enter the area, make your way right and unlock the Breathe chest to pick up the Weak Potion of the Sea. This will help you in your next task, which is to dive deep through the underwater tunnel to reach the Grotto of Courage. Before jumping into the water, drink the potion to get more airtime.

Make your way through the tunnel till you find a spot that you can dive downwards. Keep going down and trying to find ways to go deeper till you reach a wooden door that leads you to the Grotto. Once you are on the other side, pick up the Element of Courage and return to Henantier.
Test of Patience
For the final test, open the Study chest at the start of the area and pick up the Mysterious Scroll. Following ahead, you will find several pressure plates, and you need to step on the right ones to make it out of there. The scroll will show you which tiles you should step on, so read that before you go ahead.

Take note of the symbols that are repeated within each section, as those symbols will form a path that will help you exit the area. You can also refer to the image above to know the answer to this puzzle. Or you can just run across as fast as you can if you don’t have the patience to solve it. Pick up the Element of Patience at the end of the level to get out of there.
Return to Henantier and hand over all four elements, after which you can escape the Dreamworld and turn to the real world. For your efforts, you will be rewarded 6x scrolls and get Fame +1. You can check out our other Oblivion Remastered guides on How To Join The Thieves Guild, Best Early Game Sword & Bow, and Best Starting Race, Birthsign & Class.