The teleport shunt puts them in a large room. In the center of the room (and into which they are placed) is a very sturdy metal cage standing on a single pillar over a pit full of grinding, whirring, steam-belching machinery (which, as it so happens, is what operates most of the trap, natch). Thick, insulated cables connect to the cage at various points, stretching off into the otherwise bare walls of the room. The ceiling is shrouded in darkness and steam. A doorway and small landing are centered on one wall with a large sensor/speaker gizmo mounted above said. The door has no hinges or handle, and the cage likewise appears to have no exit itself.
When shunted into the cage in the loud, muggy room the sensor/speaker crackles to life, croaking out a 5 second count down. In the normal course of operations, that countdown is to allow someone who is -supposed- to be there to say a deactivation code phrase. The PCs probably won't know what it is. When the countdown hits zero, bad things go down in groove town. In order, they are:
Round 1: The countdown starts and finishes.
Round 2: Four crystaline emitters flare to life on the ceiling, wrapping the cage in an antimagic field. The emitters are quite sturdy, and well out of reach. Say 20-25' up and away.
Round 3: The machines down below start to get worked up even further - turns out the noise they were putting out before was just their idle. It's very difficult to hear or be heard. Maybe toss in a low DC fort save to avoid temporary deafness or penalty to listen checks, etc. A thick static hum begins building as the metal baseplate the cage sits on activates, electro-magnetizing the entire metal structure. Carrying or wearing metal? You're looking at a hefty DC strength check to avoid being stuck to the cage - walls, floor, or ceiling, doesn't matter. Whatever's closest. Moving from that point (or in some cases such as those folks in metal body armor, moving at all) requires that strength check. Say a DC around 28-32; roughly in line with what a Bigby's Grasping Hand's average grapple check would be.
Round 4: There's good news and there's bad news. Good news is - you know that static hum that's been growing? It discharges with a roaring crash, then falls silent. Bad news - you know that roaring crash? That would be because it just discharged an assload of electricity into the cage thru those metal cables attached to the structure, nicely electrocuting the everloving bejesus out of anyone inside. Avoiding it isn't really an option - there isn't anywhere to go in the cage that isn't rife with rich, meaty amperage, so you're likely looking at a fort save for partial damage, rather than a ref save. Anywhere between 11d6 to 20d6 electricity damage, depending on your personal tastes, with a save DC somewhere around 20, 21 or so. Basing those numbers on Chain Lightning, in case you're curious.
After that, the magnetism and electric threat are past - that level of output takes a while to charge up, after all. The AMF emitters are still on (and will be for a good two hours unless told otherwise) and the cage remains shut, however. Reason there being that the trap triggering sends an alert to a nearby guard station, and they have to release the field and cage manually. Saying the code phrase at any point before Round 4 does cause the incoming Electric Boogaloo to stand down and releases the magnets, however. Egress from the cage is managed by releasing two of the cable mounting clamps from the upper corner of the cage on the same side of the room that the door is on (search check to notice the door/clamp symmetry). When released, a section of that cage wall's bars lower, using the cables for suspension, to form a bridge to the landing by the door. A disable device check for each clamp should do (not open lock, as they're not locks in the conventional sense).
