The Undercroft River
The undercroft is a cathedral nobody meant to build. Four hundred years of water taking the easiest available route through soft limestone, and the route is thirty feet wide, black, and moving faster than a man walks.
It is not loud. That is the unnerving thing. A river this size on the surface would be a roar; down here it is a long smooth hiss, like something enormous being poured, and the echo makes it come from every direction at once.
There is a mooring ring set into the stone at the water's edge. Old. Bronze. Used.
The Way Out
Below the Labyrinth's lowest floor a real river runs from the island's interior to the sea. The maze's drains, cisterns, and floods all feed it. It is deep, it is quick, and it comes out at the cliff foot in about twenty minutes of travel — the fastest exit in the Labyrinth by an enormous margin, and the one that most punishes going in unprepared.
Two things stand between the party and a twenty-minute ride out.
- The sump. Eleven hundred feet downstream the roof comes down to the water and stays down for sixty feet. Nobody floats through a sump.
- The naiad. It is her river. She was here before the maze and she has watched the Deep Water Kin move into her lower reaches, and she is not pleased with anybody.
Requirements
| Requirement | Where it comes from |
|---|---|
| Reaching the river | Downhill, always. R002 The Weeping Cistern drains to it, R024 The Split Aqueduct is fed from it, and R014 The Drowned Ledger is below its high-water line, which is how the party learns it exists |
| Something that floats | A door off its hinges, the vat lid from R058 Cellar of the Wine-Dark Vat, pen hurdles from R008, or a proper raft lashed from R006's wing-frames. Six people needs about 80 square feet of buoyancy; a party who takes two trips is fine and slow |
| The sump | Three answers, all legitimate: hold your breath (Athletics DC 14, one round submerged, on a lifeline); lower the water by opening the sluices in R024, which drops the sump by two feet and turns it into a duck-under; or portage around it through the Deep Water Kin's gallery, which is dry and occupied |
| The naiad | R089 Pool of the Sleeping Naiad is the introduction, and she asks a favour before she asks a toll. A party who did the favour is passed downstream with her blessing and the sump held open. A party who did not meets her here, cold, and has to earn it in one conversation |
Clues
| Tier | Line to deliver |
|---|---|
| Whisper | The drain in this floor does not echo. Whatever is under it is too big, or too far, or too full of moving water to send anything back. |
| Trace | A high-water line on the wall of a chamber that has no water in it at all, three feet up, marked in silt and freshwater weed. |
| Sign | A mooring ring, bronze, bolted into stone at the bottom of a service stair — worn shiny on its inner curve by a rope that was tied and untied many times. |
| Proof | The river itself, seen from a grating: thirty feet wide, black, moving, and the hiss of it coming up through the floor. |
| Path | A boatman's tally cut beside the ring — nineteen strokes, and a sketch of a low arch with a figure crouched under it and the word breathe. |
| Door | The landing, the moving water, and downstream on the current a faint smell of salt that gets stronger the longer you stand there. |
Resolution Scene
Fifteen to twenty minutes, and the decision is the sump.
Phase one — the launch (5 minutes). Lash the raft, tie on, push off. One Survival or tool check at DC 13 for the lashing; failure means the raft is sound but sheds one item's worth of cargo somewhere downstream, and the players choose what was tied on badly.
The ride is the reward for choosing this Resolution. Four minutes of table time describing a river in the dark under a maze: the roof coming and going, drowned masonry, a chamber where the current spirals and something pale keeps pace with them and turns away, the temperature dropping.
Phase two — the sump (10 minutes). The roof comes down. The party can see the waterline meet the stone and there is no beach and no ledge and no way around.
| Approach | How it runs |
|---|---|
| Hold your breath | One at a time, on a lifeline, hand over hand along the roof. Athletics DC 14; a failure means a tangled line, one round of drowning, and a companion going in after them. Sixty feet is one round of held breath for anybody, which the party should be told before the first person goes |
| Lower the water | Somebody has to go back to R024 and open the sluices, which takes twenty minutes each way and splits the party. The sump drops to a two-foot duck-under and nobody rolls anything. This is the smart play and it should be rewarded with a completely uneventful crossing |
| Portage | Carry the raft up the bank and through the Deep Water Kin's dry gallery. No swimming, one unavoidable encounter, and the party is fighting on a ledge above their own escape route |
Phase three — the naiad. She surfaces at the sump, whether or not she was met before. If the party did her favour in R089 she holds the water down for them, says one true thing about the sea, and is gone. If they did not, she wants something small and specific — a name spoken over her water, a promise not to come back, a piece of the surface — and she wants it in one conversation, with the current pulling.
Phase four — the cliff. The river exits under the Knossian cliff at a fall of about eight feet into salt water, in daylight, with gulls. Dexterity save DC 12 or take 1d6 and lose your grip on something.
Fallback
The raft is lost, or it breaks, or nobody can hold it.
- Swim it. The river is quick but it is not white water above the sump. One at a time, on a lifeline, everybody counted twice on the far side — a Constitution DC 12 against one level of exhaustion for the cold, and Athletics DC 13 for the sump.
- Cost: exhaustion, the cold, and every unsecured item. Ask each player, item by item, what was tied on. Whatever was merely carried is in the river, and the river goes to the sea.
- If a character drops below 0 in the water, they wash up alive on the beach below the cliff at 0 HP with one failed death save. This Resolution does not drown people. It robs them.
- The party still gets out. Cold, poor, and eight minutes ahead of anybody who took the stairs.
Resolution-owned, never on the loot table.
- The naiad's leave. Whoever spoke for the party may draw safe drinking water from any fouled, salt, or brackish source, once a day, by asking. Small, and it has saved expeditions.
- The boatman's tally, prised off the wall — nineteen strokes and a sketch. Proof that somebody was running this river regularly, which raises the question of who and for whom.
- Whatever the river gave back. The sump's upstream side is a strainer for four centuries of things the maze dropped. One salvaged item of the DM's choice, plus a bronze cup with a name on it that the party will recognise.
Scaling — APL 6 / 12 / 15
| APL | Adjustment |
|---|---|
| 6 | The sump is already low — a duck-under, no checks. DCs −2, and the naiad is friendly on sight |
| 9 | As written |
| 12 | The sump is 90 ft, which is two rounds submerged, and the Deep Water Kin have a picket on the far side. DCs +2 |
| 15 | As APL 12, plus the river is in spate from the maze's own flooding: the ride is white water (three Dexterity DC 15 saves against 2d8 and being swept off), and something is in the water with them the whole way down |
- The river is the fastest exit in the Labyrinth and it should feel like it. Twenty minutes of current against four hours of corridors. A party who finds it early has found a genuine shortcut, and the correct response is to let them take it.
- Spend real time on the ride. Four minutes of unhurried description — the hiss, the roof, the drowned rooms going by, the pale thing that keeps pace and turns away. It is the most atmospheric passage in the whole feature and it costs nothing but words.
- Tell them the sump is one round of breath before the first person swims it. A drowning rule the players did not know about is a betrayal; the same rule announced in advance is a great scene.
- Reward the sluice plan loudly. Splitting the party for twenty minutes to lower a sump is exactly the kind of thinking this dungeon is built to encourage, and it should produce a crossing with zero dice in it.
- This Resolution robs and never drowns. Say the rule to yourself before you run it. Water in this maze takes your pack, your rope, your lamp, and your dignity, and gives you back your body.
- B08 parties came in through the water and go out through it, which is neat, and either the sea took their ship or it did not. Decide before the session which, because they will ask the moment they surface.
- If the party is out of time, launch, ride, duck-under, cliff. Seven minutes, and keep the gulls.