Guild Wars 2

Do you have to destroy everything by yourself or can you do it with friend? Also I tryed to kill that wall but could not in any way.

My friend and I were trying to get this and we destroyed everything in the dungeon, but no achievement.

Is the requirement that everything be destroyed while your in it or is it that YOU solely destroy everything in the dungeon?

Also there is this mini wall that looks half stuck in the hill near the NE of the zone, and after 20 mins we decided it wasn’t possible. (Is it?)

Thanks!