The Cairn of Bahar Farwind is the cairn in the Freemarch zone (levels 1-19), which is the introductory zone for Defiants.
The cairn can be found at coordinates:
5898, 5033
The maximum level of the reward is level 30, and it will be a bind-on-equip (BOE) class-specific item of Uncommon, Rare, or Epic quality.
This location is useful for the Cairn Do Achievement.