This adventure is very good to use as a startup, and to show overconfident PCs that they can be beaten.
The party is hired to deliver some important object (sword, tome, whatever) to a guy in a nearby city or town. On the way, they must cross a wide river. When they arrive at the bridge, they are stopped by 2 men with weapons, and asked to pay a toll (a big toll.) While they are getting the money, or if they refuse, they are ambushed by about 10 more thieves hiding in the woods surrounding the bridge. The 2 tollmen also attack. The enemy's weapons are poisoned so that the victims will fall unconscious very quickly. When the PCs awaken, they are at the bottom of a deep pit in the forest. All their possessions are stolen. Once they get out (it shouldn't be too hard), they are lost. After a lot of searching, have them come to a path. If they follow it, it will lead to a ruined cottage. The men who ambushed them are there, either sleeping or awake (depending on whether it's day or night.) The PCs will recognize them and (hopefully) plan to ambush them to get their stuff back. This time they outnumber the bandits, and have the element of surprise, but are unarmed. If the bandits are asleep, there is only one on watch, and the party should win.