Park at the S curves 4.2 miles up Big Cottonwood Canyon on the S side of the road. From here follow the creek to the E then follow the summer trail into Mill B S drainage. This heads up for several miles through aspen groves until you hit the lakes. From the lakes branch to the E/left and continue staying to the left most branch until it terminates in the uppermost cirque. From here you'll see the deep gash that's formed by the Heart of Darkness. Head to the left putting in the skin track to the ridge and then traverse to the top of the chute.