The other guide is way too vague.
Before completing the War Table mission "Liberate Emprise du Lion", you need to go to options and turn on Rest Easy in the trials menu.
Then head to the map. Follow the liberation questline and destroy all the camps and claim them. Playing on Casual will help you along and you shouldn't need your focus abilities to finish it.
I completed it at level 8. (was level 10 at the end of the questline).
Two mages (One fire, one a Spirit build with Ice as their damage skill), one Battlemaster Warrior using sword and shield (preferably Blackwall) and a rogue (I used Sera, but found Cole can be very useful when I tried it again with him).
You can skip two battles on the way up, the Second troll battle by heading straight ahead and then following the wall around, then you can skip the next battle by simply running through the door at the top of the stairs and waiting at the next doorway.
The last battle cannot be skipped and needs to be played. Make sure the shadow dies first then the marksmen, as they deal the most damage.
When it comes tl the boss. If you're not worried about pissing off every companion at this stage. You can just accept the Demons offer and claim the keep, after two cut scenes the trophy will pop.