Having heard a rumor of a strange mage still wandering the Storm Coast right after she'd finished conscripting them all into the Inquisition, Kubrie decided this aggression would not stand. First, she went calling at his house, but no one was home. Worse, he'd left a locked door, which is a challenge to any self-respecting looter, but the lock couldn't be picked, which is an affront to any self-respecting looter.
So, the gang -- Blackwall in place of Varric this time, and Vivienne in place of Solas -- went in search of the renegade mage and the key to the locked door.
He wasn't in the Astrarium Cave.
Nor disguised as a Mabari.
Nor down this path, which looked vaguely familiar...
... because it led to the Cabin they had just started from. Crap.
Kubrie wished Varric were here right now. He'd say something clever about how they meant to return to the cabin in case the mage had come back.... or something. Sigh. Bull tried his best and struck up a conversation that went like this:
Iron Bull: Hey Blackwall. What's the most limbs you've ever cut off something in one swing?
Blackwall: For the Wardens, battle is a sacred duty, a vigil kept to guard the world against destruction. It's not a game.
Iron Bull: Right. Same here.
Blackwall: Do heads count?
Iron Bull: Heads absolutely count.
Blackwall: Then... three.
Iron Bull: Nice! Down on the collarbone and through, right? That's how I get the good ones.
Well... Kubrie thought it was funny. Maybe it's a Qun'ari thing. Then Vivienne complained that the weather had ruined her outfit and it would have to be replaced. They got back on the trail. As you can see it led them everywhere. I marked the cabin with a waypoint, and just kind of wandered around, actually hoping the mage would be nearby. The quest marker is for one of Blackwall's "Memories of the Grey" which is the reason he's on the quest instead of Varric.
The gang decided it was time to go after those 'memories' and see if they ran into the mage along the way. "We're off to see the wizard, the wonderful wizard of... err, the Storm Coast, with the key, for the locked door... *ahem* "
Blackwall says: Looks like the mage isn't at the bottom of this big cliff.
Blackwall says: The mage is probably not in that crevice, either. Just a guess.
Okay shorty, that's it. You're not the least bit charming even if you do fill out that grey warden armor nicely and your beard is strangely alluring. You can go hang out with the horses from now on, get me?
We still haven't found the mage, but we did get the first of Blacwall's 'memories' and continued toward the second. On our way, nearing that Big River, we did find this, which is a first for me. Maybe I'll get the whole collection this time.
Finally, after collecting the second of Blackwall's 'memories', we found the mage, out for a stroll without a care in Thedas. So we killed him. And took his key. And returned to his home. And looted it. Unfortunately, the majority of the fight with the mage was obscured by a giant tree and I didn't get any really good screenies of the battle.
It was a fun little distraction chasing that guy down. We collected a fair bit of summerstone and serpentstone and elfroot, fought some mabari and a couple of bears, and found that bottle of booze that I never knew was there before. Kubrie also reached level 11 and we got a new potion to try out.

Thanks, Melbella, for bringing this to my attention. As for this:
Besides, you know you want to get ALL the achievements, right? 
Pure evil

...j/k
Thanks for the tips on NM, from and you and everyone. Maybe I'll try a NM run for the Cullen romance PT.
EDIT: Forgot to add a pic that shows the location of the mage's cabin and our wandering path around it to find the mage. Oops.