Here's a guide on where to find everything for the achievements for Northern Arun.
Lost Clues Find a Puzzling Monument in the Sundered Cave in Ex Prima
First you'll want to follow the map to where my location was, it can be a bit tricky since there's no clear route on the minimap.
This might help to show you exactly what direction to take once you get to that little mini-bridge.
This Monument was a pain because you have to interact with it and some people said they had to wait around a minute or two for the achievement to pop up, so be patient.
An Ancient Puzzle Find a Puzzling Monument near the castle's gate of Arx Umbra
Teleport to the only camp in Arx Umbra and either use the Teleport Platform to go to the platform or walk to the castle, either way! :)
Once you cross the bridge that's constantly getting shot at by cannons, immediately take a right and go all the way down, the monument should be at the end.
Highest Marks Climb the hills north of Highwatch and find a Wall of Wordcraft
Follow the red marks and u kinda have to wall-jump to get up those mountains. Once you're up just run straight towards the platform in front of you. Once you get to the platform just take a right and youll see the wall of wordcraft there!
Ain't No Mountain High Enough Reach the Highwatch Wall of Wordcraft
This one is odd in the fact that there's no actual Wall of Wordcraft here? You just go to the spot I'm standing on the map and move your camera around a little and the achievement should pop up.
Make sure you're standing at the part of the gate thing that's broken when you do this or you won't get achievement. Try and stand where I'm standing.
What a View Find the Wall of Wordcraft above Boscan Terrace in Savage Reach
Start at the camp and move towards the direction of the red lines, once you get to the opening with a crapload of mobs, go straight and there will be an opening in the back where you'll be standing on a wooden platform.
This just shows the direction you're coming from. Once you get to where I am just keep going up the ramp and youll see the Wall of Wordcraft!
And you found it! :D
Credits: Special thanks to Flustered for making this North Arun Achievent guide.