"Frida's Dilemma" - "Negotiations" [Campaign 1, Mission 4]

In the game, you can't enter there! Not far from the first garrison, there's a keymaster's tent! Go there, and travel south from the first garrison, heading east!!! Keep going; you should find fire drakes! Defeat them and continue; the entrance to the dungeon is there! Enter, travel a bit, and the mission is complete!