< Diablo
At caves level 10, back to town and talk with Griswold. He will say something about an magic anvil that countains demonkind magic on it, however, that was just a legend that was told to him. But he will ask us to check it, and, if is true, maybe he can get something for us as a reward.
Backtrack to level 10 and search for the anvil, it will be somewhere here. When you find it, back to town and handle it to Griswold. He will get amazed, the legend was true. As a reward for you, he will make you - using the anvil's magic - the unique item: Griswold's Edge, that is very powerful.