The Prison of Seven Cells

The long-sealed subterranean prison beneath the Grey Vale Cave, built by the vanished pre-Rivalon race to hold their most dangerous enemies — the place Otto came to find and Thalia's Primeval Awareness flagged in Session 25 (seven powerful creatures: the Queen above, six below). It lies roughly half a mile to a mile down, reachable through the cave's flooded groundwater chasm — a ten-minute swim now open to the whole party thanks to Silithane's Water Breathing. Much of it is flooded (difficult terrain for anyone but a swimmer); rooms hold rusted decorative armor on stands, mouldered tables and chairs, and cell doors (one a notoriously stubborn pull-door).

The Queen Grabbler is believed to have broken out of one of these cells and crawled up to the cave, growing too large to ever return. Six prisoners remain — among them, the party learns, one wrongfully-imprisoned woodling sprout. The lizard-people The Grenkh have colonised the outer cell-rooms as nests and appointed themselves the prison's reluctant guards; the deeper jail door (to the jailer Half-gore) and a sealed bottom door can only be opened by their ruler Grank.

(In Session 25 the Mush Mother called its builders "scaled, clawed men" who hauled coffin-like boxes in and never left — likely the ancestors of today's Grenkh. Strongly echoes the Ankley Island "prison of our enemies" — same network, or a second one? See Canon Questions.)

Session 26

Entered for the first time — Lash swims down the flooded chasm, breaks open a stuck pull-door, and discovers the Grenkh tending egg-nests in the cell-rooms.
The fleeing water-group (chased by the Queen) escapes into the prison through the gap, surfacing among the Grenkh.
The party meets Grank, is granted passage to the jail, and learns the layout: the Queen's empty cell, six remaining prisoners, a captive woodling sprout, and the locked jail and bottom doors only Grank can open.

Session 27

Explored in depth. Beyond the entry rooms the party finds a throne-and-altars worship room (a stone pew, six or seven empty stone altars, a throne a magical creature once sat upon, and crates of blacksmith scrap), the jail of six glowing cells, a central chamber of overturned minecarts, the Watchers' corridors, a digging golem's tunnel-warren, and Malifax's four-room workshop.
The six prisoners named. Above each cell an engraved token: the Mad One, the Ruined One, the Sad One, the Cursed One, the Blind One, and the Nice One. The escaped seventh's token had rubbed away — Malifax confirms it read "the Needy One" (the Queen Grabbler). The cell-doors are glowing magic portcullises; the lizards' spiked barricade is only "for comfort."
The prison is an imitation. Per the Nice One, this cell-block is a copy of an older, now-flooded prison built by the Elder race (scaled, horned, hooved); the prisoners have been rehoused four times (original guards → ~three friendly Watchers, who refused release "for fear of the Old Ones" → the Grenkh).
The sump-system. 8×8 ft metal "manhole" lids bearing Malifax's maker's mark cap an ancient pipe/drainage system that predates the raiders; effectively unopenable. Silithane reads them with Comprehend Languages; Jex's "born in a tube" memories stir.
Malifax, the skinless lich-smith who forged the cells, is found and befriended (workshop opened by Lash's scrap-key). The Watchers are pacified by the Woodling Den sigil-staff; a freed digging golem roams the tunnels. The session ends on a bug-swarm in the workshop's pipe rooms.

Session 28

More of Malifax's domain mapped: the Ghoul Tamer's room ("Please knock / Ghoul tamer"), the Watcher corridors, a secret door behind a non-aggressive crab, the central minecart chamber, Malifax's cupboard/treasury (a meteorite-cracked ceiling, the loot chest, the past-showing mirror, his twin swords), and his living quarters / "other room" — six beds and a kitchen, where his estranged immortal clique and their dead are kept.
The golem-carved crack now serves as a shortcut linking the workshop to the jail side, bypassing both the Watchers and the chasm (Malifax realises he commissioned it himself).
The bug rooms are cleared (a one-sided wasp fight), and the Prisoner-Moving Staff is recovered from the cupboard and lent to the party.

Session 29

The "other room" cleared and converted. The four-room domain of the immortal-raider council — six beds, a kitchen, a junk cupboard, a binding council table, and a pointless curtain over a bare wall — is emptied of its occupants (by diplomacy) and then knocked through by Malifax (walls and door smashed with the Prisoner-Moving Staff) to become the Queen Grabbler's future cell.
A hidden room found. Behind a heavy cupboard in the council room, Silithane (nat 20) uncovers a long-disused cobwebbed door; burning the webs gives Jex a lung disease. Beyond lies the Shushu's workshop — a sealed chamber with a powerful, ancient pink teleport altar and a cobwebbed lever.
The teleporter link. The Shushu indicates the altar sends a traveller to the crab room elsewhere in the under-prison (confirmed by the GM), but warns they may not arrive as themselves — a possible tie to Valmora's dead-gods quarry. Left unpulled.
The Watcher guards are confirmed to be warded by an Elder-race "you work here" badge (the real version of the Woodling Den sigil).

Session 30

Its true purpose, revealed. Via the janitor Gerald, the place is named a "low-capacity rehabilitative detention site for minor offenders," run on a rehabilitation-first doctrine since "a time when there were multiple suns in the sky." Every inmate is here for the same crime: stealing and drinking Ambrosia, the immortality elixir.
The ice. The facility's worthy drink the Ambrosia and are frozen in the ice to survive a coming meteor, then thawed when safe — a cryo-vault elsewhere, where Gerald's wife Alice sleeps.
The raid, dated. The collapse of normal operation is pinned to the raid: raiders killed the staff (guards, the two maintenance workers, the therapists), stripped the walls and doors, and sold everything; the Grenkh lizards have run the place "for generations" since.
The shrine room. Valmora studies a stripped worship room of seven stone pedestals (grouped four, two, and one) — and, praying at the absent eighth space, makes contact with a third living god (see her note).
The Mad One is the therapist. Valmora's investigation reveals the Mad One is no inmate but the prison's therapist, left behind when an inmate escaped in the raid — kept alive by the Ambrosia therapists were given to tend immortals, and broken by ages of containment.
Building the Queen's cell. Malifax works the cleared "other room" into the Queen Grabbler's cell (~2 days); it will need two functioning gates (one corner can be wriggled behind), and Jex fills the room behind it with rubble to reinforce the wall.

Session 31

The prison reclaims its escaped seventh. After the session-long battle above, the subdued Caressa is floated down and locked into the new cell (built from the old council room) with the Prisoner-Moving Staff, the warding glyph lit — the campaign-long re-caging plan finally complete, and the Grenkh's century of guarding her empty cell resolved.
The denizens meet. With the threat gone, the prison's residents gather openly — the Grenkh stunned to learn there is an "above" (they thought their level the highest point in the world), the woodlings meeting the eye-creatures from their cave drawings, and Gerald baffled by everyone's painted "I work here" badges.
The entrance question. The cave-dwellers debate whether to collapse the cave mouth for security; the Grenkh split ~40/40/20, Gerald favors sealing "a prison, after all," and the party leaves the choice to those who live there. The six other prisoners remain caged pending the party's decision on whom (if any) to free.