Once again, this one is pretty easy to answer for me. The first game that I played was also the first one that I GM’d.
I still remember the Oldenhaller Contract, in which the heroes had to venture into a gang’s hideout only to find that they had just had a big fight with another gang. Eventually, the heroes found their way into a cave and then faced down cultists who summoned a demon of Nurgle. A real grotesque one that could kill the party rather easily.
My fondest memory was the front door. Depending on whichever way you turned it, there was a 50/50 chance that it would trigger a trap door. Our friend Patrick’s character actually DIED from this trap early on and its still a recurring joke (whenever his characters, regardless of game system or campaign, would come to a door, we still ask him which way he turns the handle).
Good times! Great game.