River in a gorge, need to carry to boat through the cascades. The cascades are a river crossing. Caves with goblins.

In game it was like this. The party decided to ambush the bad guys. They've heard about the caves near the cascades, a perfect spot. It turned out that the caves were inhabited by the goblins. The party decided to convince to goblins to help and the goblins agreed. All went well until one of the bad guys took off his cloack and revealed a feathered dress. The goblins changed sides, because there was a legend about a feathered man that will come to lead the goblins to great victories. When the feathered man was killed the goblins changed sides again and that was the end of the bad guys.
The goblins helped as much as the party neaded, some were washed away to show the players that the river is dangerous.