4. Dry Canal

If heroes linger on the canal, four cubeworms attack from below. Heroes can detect movement in the cracks between the huge canal stones with a 3|6 Maneuver challenge, taking -1 awareness on a struggle. If heroes fail to detect the worms, the monsters strike first automatically. 

The worms ignore Shinarians. If a worm takes lethal damage, it retracts beneath the bricks and stays there for three turns. At your discretion, you can make the number of cubeworms match the number of heroes, or make the worms more or less aggressive. 

Heroes can Climb out of the canal to escape the worms. If heroes want to cross the canal later, they can avoid the worms by throwing rubble down, luring the worms out of their bricks, and then quickly crossing at another point.