» Fri Jun 01, 2012 2:43 pm
In my experience, "cleared" often means killing off a particular high level occupant (the "boss" of the location, even if there are lessers still remaining). Other times, it simply means clearing it out, like some animal caves. It varies.
"Clearing" Swindler's Den may be tied to a quest. Can't say for sure. In the long run, it doesn't matter. There are plenty of clearable locales not associated with quests, if it's the achievement you're after.
I've never even been to this cave, and I got "Delver" a long time ago on my first character.