Bloody Baron - Velen
Depending on what options you chose in dialogue during The Nilfgaardian Connection quest how you have to handle this quest changes. If you faught Baron's men at the Inn then they won't grant you entry and you'll have to sneak inside. If you didn't go to the Inn at all then you'll have to give the guards some Crowns to let you in.
If you faught Baron's Men and need help finding the back entrance to complete this quest then use my screen shots above and below these paragraphs for further guidance. Even if you are allowed free entry into Crow's Perch I still strongly recommend you go through the cave mentioned on this page as there is a bunch of good loot in there as well as Crafting Recipes.
Use the Torch if you're having trouble seeing where to go inside of the cave; to proceed through it you'll need to climb up multiple cliff faces that will lead you to a ladder that you climb up. You'll find multiple crates/bags/boxes throughout the cave that you can loot - use your Witcher Senses to easily locate them.
Regardless of your path inside, once you speak with the Baron you'll get a cutscene and the quest will complete. You'll also be immediately thrown into another quest where you control Ciri called Ciri's Story: The King of the Wolves.