Recently I terrified my players with a completely normal elevator. They're stranded on an island in a homebrew fantasy setting full of ancient ruins. While exploring one at the behest of an undead king, they encounter a small dead end room with a single button in it. Upon pressing it, the door to the room closes by itself, sealing them inside. They hear grinding mechanical sounds around them, and they suddenly feel strange feelings in their gut. I spend several minutes describing everything in detail, from the slow closing of the doors to the faint feelings of motion, and they're absolutely freaking out at the table, thinking they've let themselves fall straight into a death trap, when... the door opens again and they're on a different level. I think it's the pinnacle of my (admittedly short compared to some people) career as a game master.