This is an unmissable story achievement you'll unlock early in the game. After you head down into the cellar at the start and kill the rat, you'll be attacked by a giant flame-breathing rat. Run back upstairs to have the fire put out. Head back downstairs and you'll encounter a man who will teach you the the Thunder Spider song. After you are done with him, play the song to summon the spider, then head back to the large rat. The spider will kill it and you'll unlock this achievement.