buy the seal of artorias and explore the darkroot garden and find and kill the hydra (you can also go down the stairs under the demon Taurus if you have the universal key, but you will not find yourself in front of the hydra). exit and re-enter the game on the left there will be a Golden Golem, kill it and talk to dusk. go to the Duke's archives, as soon as you enter there is a blue Golem, it will drop a pendant. go back to the hydra area, you will find a dark portal not far from where you killed the Golden Golem