Greenskin Gorge

From the Introduction:

Greenskin Gorge is a standalone encounter designed for five characters between levels 4 to 6. A canyon full of goblins, orcs, and trolls is infamous for its many ambushes—few that enter the gorge escape without a hostile incident. A nearby merchant outpost has had enough of the harassment, and tries to enlist the PCs to help in an ironic turn of events: using the gorge’s many hiding spots to set an ambush for a convoy of goblins as they return from raiding a nearby caravan.