I have spent so much time clicking every possible thing and trying everything I can think of for some of these quests / hidden areas. If anyone wants to help solve some mysteries with me, I will point you in the right direction and maybe you can be the first to solve it! I might miss some info because there is so much, but here is a good summary of what I am pretty sure are huge keys to solving some of these.

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1. Lighthouse:
   1. Corvo lighthouse - "Lighthouse Keeper" found dead in lighthouse. You can use the brazir on top of lighthouse and it goes out and starts event. Lighthouse quest gives glasses/trinket that you give to npc Varner Barsavi in margrove. He tells a story about someone running from saltdusk keep, going into a spider cave to hide. This door glows at dusk and dawn on CHANNEL 1 ONLY. It can be opened by right clicking the hidden button in rocks to left of door. This cave is filled with brotherhood npc's, completing event kicks you out nothing happens and NPC acts like you didn't find it / the secret.
   2. Harbor island lighthouse - "Lighthouse Keeper" is a wraith, the light went out on lighthouse and people died including his wife. He washed up on shores of harbor island? You kill his wifes spirit and put her to rest. His wife's name is Hope. He mentions foggy / rainny weather and night, so event probably only can happen then. In basement where the event happens, there is a scene that matches corvo lighthouse. Sword in corner, below it unlit torch, to right box, below that corpse of corvo lighthouse keeper leaning against it. Harbor island is a board leaning against it.
   3. Honorable mentions - Mariners Spectre is a resentful spirit? hill in Gallowstown is called Blood Mountain. Right clicking the camp fire in hut lights it and summons him when ??? conditions are met. Doesn't seem to do anything. Under blood mountain is hidden zorean area. Zorian oil is used to light corvo lighthouse, could be related.

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1. Brotherhood

2. Brotherhood Feather (probably part of lighthouse quest) - This is given to you by (a member of the brotherhood?) a npc in saltdusk keep prison. He tells you "There's a cabin in the woods north of the Corvo Lighthouse. We have a fence there. Show him that feather, and he'll do buisiness with you." There are a few cabins in woods, no NPC in sight.

3. Brotherhood have taken over the hidden "Spider dungeon" mentioned previously. Completing it does nothing? and Varner Barsavi acts like you didn't do it.

4. Bentbow hideout - Going near the left side of hill there is a ladder down. They swarm and spawn ontop of the hill because you got close to their hidden hideout.

5. Deeper Rohna is lvl 36-38 brotherhood members. All the doors are locked and no one has found the key.

6. As part of deeper Rohna, or between deeper Rohna and bentbow hideout you can see a lvl 74 brotherhood npc (hostile).

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1. Hookmask camps

2. Ravencrest Grove - Just outside of Ravencrest is ravencrest grove, listed as a lvl 6 to 32 zone. Interestingly the hill behind Jensens house has a statue of Odin, and cave is filled with dwarf statues for some reason? The hostile NPC's are lvl 8 hookmasks. Exploring that we find 2 different places to use lighthouse grappling hook. No obvious way to go down there though. Completing ravencrast grove event can reward hookmask key.

3. Hookmask Camps / Hookmask key - Going underground with the key you can access a lvl 38 hookmask area. Pour wine into the 4 basins and start some drunken ritual event and doors open and let you go deeper into area. You kill a ton of hookmasks who are defending something? I clicked everything and pressed F on everything and found nothing.

4. Hidden floor beween two previously mentioned zones - There is a floor of a cave that I have not been able to find access to. There are 2 exits from it, using the previously mentioned lighthouse hooks. Part of the area above that floor is the 38 hookmask cave, and a rock blocks path to the rest of the cave above it. I tried for hours and found no way to get into that cave and have explored every nearby cave as well.

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1. Skorn

2. Chaple of Skorn - Past Astor demon you kill, if you have the lava boots from dragon quest in hadarak desert you can cross farther and find lvl 44 demons. I found nothing clickable in this cave systems.

3. Below Gladmire fort - lvl 40 Skorn are in this area, and there are lots of locked doors. A key probably exists if someone has found it.

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Hopefully some other people are as invested into this as me, and maybe this will help! I will gladly take some hints, we are just a couple of pieces from solving some of these mysteries.

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