The Nightmare Express

Underground like the colored lines, but with wider tracks, no electrified third rail, and a platform roughly twice as long as the already-long Red Line one^B3C4

Cab Controls:

A red throttle lever, a whistle chain, and two separate braking levers, one for the engine and one for the cars behind it. Five pressure gauges track the boiler, which can overpressure into a lethal explosion if mismanaged. A hinged, lance-tipped pole mounted on the driver's side swings out to hit track switches, usable only at low speed. A small backup fuel box near the exit works without water or oil, enough only to limp back to a station and vent pressure, not to run properly^B3C14

Rolling Stock:

An old-school, jet-black steam engine, coal or possibly magic powered given the lack of a third rail, with 666 painted in red on the front of the boiler and a wedge-shaped cowcatcher below it. Pulls about forty cars: fourteen open-topped ones seen holding massive, caged monsters, the rest rickety empty freight cars with no doors facing the platform. Only two cars allow boarding, the rear caboose and the forward passenger car right behind the engine, and the passenger car's own door reads exit only, forcing anyone on board to enter from the caboose^B3C14

Idling a few stations down the hidden employee line, its last confirmed use having been ferrying Brynhild's Daughters to station 60; two dwarven engineers climb in through the broken side window wanting to take it somewhere before Fire Brandy turns them away^B3C31

Finally pushed through the Station Repair portal, every car making it across intact into Station and Repair Hub E, before Widget unhooks the wrecked cars from the engine to free it from a dead-end service bay. Leaves the yard as just the engine and its forward passenger car, towing nothing for the first time since Carl took it over, and stops again at the tunnel's station 24^B3C17

The Station Repair switch examined up close for the first time: a pass-through, two-way portal gated by conveyance or key rather than one-way like the Abyss's own, with the track physically running through it into a branching root of far-side tracks. A near-twin red-painted train crosses through under its own power while Carl watches. Recycle only reaches the Abyss and Auxiliary Tracks would strand them on whatever track that red train just used, leaving Station Repair the only real option left, though still untaken as the chapter ends^B3C16

Confirmed running through a switching cavern with Auxiliary Tracks, Station Repair, and Recycle switches before terminating at Abyss Station, #436; Carl leaves all three switches untouched and stops there on foot instead^B3C15

A five-stop figure-eight loop that returns a rider to their start. Four of the five stops are ordinary transfer stations; the fifth, station #436 at the very top of the figure eight, isn't a transfer station at all. Per its own sign at station #83: this station (yellow and red lines), then station 283 (mauve and purple), then 436, then a different station 283 (green and yellow), then a different station 83 (tangerine and plum)^B3C4

Comes once every hour and a half; the party misses its pass while inside Limp Richard's shop^B3C4

Over a hundred miles an hour under full power, closing a quarter mile in a matter of seconds even while braking^B3C14

Carl:

Drives it through the Station Repair portal, gets routed into a dead-end service bay, and escapes Station E's yard once Widget and Donut get the turntable working^B3C17

Stops just short of the Station Repair switch to examine the portal and take a screenshot through it, then turns the train back toward station 283 without crossing^B3C16

Stops the train at Abyss Station to explore on foot, then drives it roughly two hours back toward station 283 to reunite with Donut and Katia, still towing the mob-filled cars behind it^B3C15

Boarded for the first time, disastrously: gets hit by the cowcatcher after a failed shield-and-teleport plan, is carried past the platform into the tunnel, then fights his way into the cab and ends up in control of the whole train with Fire Brandy's help^B3C14

Plans to wait for his Protective Shell spell to reset before boarding, intending to clear the whole train of mobs with it rather than risk the unknown; stages at station 281, two stops short of the transfer station, still not yet tested^B3C13

Wants to see the train and examine its sign, but the party decides against boarding until they know more; relays the confusing route math to Mordecai in disgust^B3C4

Fire Brandy:

The Lesser Demon sealed into its boiler as fire-stoker, revealed once Carl breaks into the cab and she pokes her head out through the firebox door to talk him through actually driving it^B3C14

Widget:

Unhooks the wrecked cars from the engine and works the turntable to free it, dying to a revived ghoul before he can ride out with the party as planned^B3C17