The Abandoned Burrow
The Abandoned Burrow is a cave filled with insects, west of Saliko Village. It can be completed alone at level 3, or by a group of adventurers.
Most hazards in this dungeon consists of a variety gnats, and should not pose much of a threat. That said, it is still well possible to get knocked out by pulling several groups of monsters at once.
As long as you take your time however, and let yourself heal up every once in a while, you should be fine.
The one and final boss of the abandoned burrow is Zandra, a level 6 insect. She is surrounded by four gnats that guard her. They can be attacked without getting Zandra's attention. Engaging Zandra will cause any remaining guards rush to her help, which is the objective of the "Nothing more than gnats" trophy.
The Abandoned Burrow is not an actual dungeon, but rather an instanced area with a boss at the end. As such, you will not be bound to the dungeon if you defeat Zandra, and can run it again after a short while if desired.