After you pass through the start of the Magic Crafters homeworld area (you should reach the 2nd dragon), turn back, and head towards the start of the homeworld -- where the balloonist dropped you off.
Once you're entering the cave at the start, you'll see 4 armored druids form a diagonal line.
To trigger this achievement, run through them all in quick succession. The first one will try to attack you when you get close, so keep that in mind, but if you time it correctly you can run through all 4 without taking any damage.