Tundis can be found by the zone in to the Fallen Gate, which is in the far northwest of the commonlands zone. Speak to him and he will ask you to prove yourself by gathering 5 boulders from sandstone giants. These giants can be found in the maze that leads from the open commonlands to the fallen gate zone and a full group of mid-teen level characters is required to hunt them safely. Once all 5 boulders ahve been collected, return to Tundis and he will send you back to Kanos.

When speaking again to Kanos, be sure to have a group ready for the instanced encounter that you will be sent into. See him in north freeport and you and your group will be transported to a zone which you must clear in order to win the quest. Once this has been done, zone back to north freeport and collect your reward and flag for acess to the fallen gate.