This quest begins immediately after Gathering Strength. Now that you’ve reported to King Flann, it’s time to speak with Eivor’s cousin, Barid, at Knockfree.
Find and Speak with Flann’s Scout at Cashelore Castle
To reach Flann’s scout in the easiest way possible, you should approach Cashelore castle from the southwest. You’ll find the scout waiting just beneath the bridge on this side. When you speak with her, she’ll suggest that it would be folly to scale the walls with so many guards at the ready, but that it would be possible for a wily vikingr to find a way in.
There are numerous ways to infiltrate the castle, but the safest way is to climb the tower and then climb down to the bottom from inside it. Here you’ll have a chance to use Odin’s Sight and view any nearby enemies that might need to be taken out. You can actually get beneath the tower without having to kill anyone if you time it correctly, but this will require avoiding the Standard Bearer who regularly patrols in and out of the tower.
Alternatively, you can wait for the Standard Bearer to enter the tower and then assassinate them before they alert any other guards. To do this in one hit, you’ll probably need the Advanced Assassination (Way of the Raven) skill. You can then do the same for any other guards that you encounter as you make your way to the door. If you’d rather avoid having to engage in stealth and assassinate guards as you go, you can just run to the gate from within and shoot the lock on it. This will trigger a cutscene, during which the castle is breached by Flann’s army.
Take the Southern and Northern Ringforts
The assault on Cashelore castle is relatively simple. There are no special phases of the battle which involve battering rams or opening drawbridges. Instead, you just need to kill all the enemies within the southern and northern ringforts. This should be an easy task since there are few elite enemies, especially with the aid of Flann and his army. All you need to do is completely eliminate every enemy within the castle ringforts, including those on the ramparts. When all the enemies are dead, the assault on the castle will be complete.
Find and Speak to Ciara
Once you’ve taken Cashelore castle a cutscene will play, detailing a bit of the aftermath celebrations. At the end of the scene, you’ll need to find Ciara at the base of the tower nearby. You’ll hear her singing, but you can use your bird and Odin’s Sight to reveal her location more clearly if necessary. When you speak with her a cutscene will play out, during which you’ll have the opportunity to begin a romance with Ciara, but it doesn’t go anywhere yet. If you’d rather not romance her, it doesn’t matter which of the other dialogue options you choose, as the outcome will be the same. After the scene the quest will complete.