The path is initially blocked by a stone grate located in the ditch surrounding the map. To open it, search the map for round stone buttons, and step on them at the same time. If a message about an ancient gateway shifting appears, the gate has opened. You only need to press them both at once, they don't need to remain pressed afterwards for the gate to stay open.
Kjaro, the Blazing elite, and Runald, the Glacial elite, are tough and use powerful ranged attacks. Close by, they will use a short-ranged but extremely powerful firebreath attack. Both attacks, especially from Kjaro, may be lethal. Bringing a friend to battle is recommended.
The challenge can be completed in singleplayer by placing turrets on the buttons as the Engineer, rolling an explosive pot onto one button and stepping on the other, or by forcing an enemy to pathfind across one button while you stand on the other.