If you explore Sawmill with Spirit Vision activated then you can meet Lifewood, a ghost of an Elf that is contained in a tree. Speak with him. He asks you to avenge him and kill the person that cut him down.
The lumberjack is dead but you can exact revenge on his ghost. In order to do that you must cross the bridge and head towards traps. There, you can find two graves.
One of them belongs to the lumberjack. Dig it up and a ghost will appear. You must absorb his energy.
Then, you must go back to the tree and inform the ghost that you have avenged him. The Elf is thankful to you and rewards you handsomely.
Reward: 36,100 experience points + 2 guaranteed rewards + 1 out of 5 that you can choose from depending on character's class + Lifewood Shield