From what I recall. You need to go to the dark swamp first to find clues, then go to the misty abyss. The map will show you where you need to go -> (!). Just go to the top right at the edge of the map. After that, report it to logan.
(Warning ⚠️) If you want to have a relationship with Logan and see his kind smile. Complete his second heart first before completing the "trouble in the den". I HIGHLY suggest to ignore it completely until you complete his second heart.
You should see what you need to do to get his second heart by going to the book, and relationship log and checking his "love". From what I remember, is to complete the Bareshade expansion, Country Road, and (I think?) Curse of Lust first.
Having a relationship with him will open two different sex scenes whenever you visit him and ask to workout with him. Choose the "admit you're watching" or something like that and help him work out instead. Choosing the correct choices will give you access to feel his muscles and you know the rest 😉
Remember to keep saving when they are some choices in the game or if you think it's a great idea to save the scene in case you FORGOT something you need or if you MESS UP. There's no back button to reverse your mistakes 😀