Agony

Make your way to the end of the first chapter or load up The Guardian of light, you will find yourself in an area with a spider and some madmen to the right. The first heart is right where you entered from on the floor. The second heart is right by the exit, and a little closer to the exit (past that purple glow) is the third heart. The last heart is with the group of madmen. Make sure you grab a torch before placing the hearts in the scale near the Baphomet. The cutscene will go off and you will be chased around the area. Find a crevice with an easy way around and run through it when the Baphomet is close. This will distract the Baphomet giving you the weak spot, his back, run behind the Baphomet and burn him with the torch three times for this achievement.