Kind of a lazy morning here, so I thought I'd post a piece I was editing for the Black City. It shows the huge gap between jotting quick notes for use in a home game, versus the amount of text you might need to explain to someone else how something should work in game. The first floor of the tower feature features a gate opening mechanism where the aliens mechanized a ritual to summon a Lovecraftian entity; that's one of the themes in the ruins, not necessarily original, the exploitation of dark magic and how it's gone horribly wrong and created these sprawling ruins.
For contrast, the previous write up of the Tower of Astronomy, back when I was brainstorming, is part of this old post: B Tower of Astronomy
B Tower of Astronomy
The Tower of Astronomy is a twisted spire of impregnable black rock looming over the southern part of the city; a long stair climbs to the sole entrance, a doorway 50' above the ground, where a pair of Watchers (orange level) flank the door. The Watchers fire force beams from their eyes, forcing a save vs paralysis to avoid being thrown off the stairs, in addition to the normal damage.
Beyond the Watchers are large half circle doors (orange) of permalloy that retract back into the walls allowing access when a passkey is presented. A spiral pattern is engraved on the doors.
The Inhabitant from Carcosa
The only creature currently in the tower is a wraithlike spirit that became trapped here after crossing into the tower from the gate to Carcosa. Passage through the gate drained much of its animus, so it appears misty and indistinct with pinpoint eyes. It hides in alcoves and watches from a distance, ambushing a victim after a group splits up to explore or is distracted by the mahcinery. With each successful level drain attack it makes, it's appearance solidifies to portray a haggard man in Renaissance finery. After two successful drains, the spirit has enough vigor to pass back through the Carcosa gate. In life, the thing was a noble from a doomed world absorbed into the corpse city of Carcosa, and the ghost is a thrall to the King in Yellow. After crossing over, the ghostly nobleman makes his way across the Lake of Hali, to report to the King about the gate. A serious foray from Carcosa is soon made when the King learns of the new world to spread madness and despair.
Ghostly Nobleman of a Doomed City
[ Omitting the stat block, uses stats as a Wraith ]
Lower Floor - The Gateway Apparatus
Directly across from the door is a large, arched portal, obscured by flowing mist. To the left of the room is a broad stone table, stacked with metal tablets. The center floor is dominated by a pair of nested magical circles inscribed on discs. Running along the right side of the tower is a complicated mechanical mechanism comprised of tubes, cables, and armatures; the mechanism arches into the air high above the circle and also projects upward through the ceiling. The mechanism thrums with power. All of these areas are further detailed below.
The Thaumaturgic Circles
The interior of the tower is glistening black rock, polished to a mirror surface and highly reflective. The floor is made of basalt blocks, but the central section is a 30' diameter circular disc, slightly raised above the level of the outer floor. A thaumaturgic circle and a five-pointed star are carved into the large disc. At each point in the star, there's a small platform for standing, and a hand post topped by a crystal globe. Within the center of the 30' diameter disc is a smaller disc, also inscribed with thaumaturgical circles, but this circle contains a stone rectangle with a manacles.
The stone rectangle is long enough for a human to lie on, and there is a body-cavity depression carved into the stone surface. There are two pairs of manacles, for ankles and wrists, and when first encountered, the manacles are open. They clasp firmly on anyone that puts them around a limb, sealing fast with no apparent mechanism. They are enchanted adamant, and are impregnable; only a Knock spell frees a captive once a manacle is closed.
If a character approaches the portal, the mist dissipates, and a scene along a mournful lakeshore is viewed through the arch. Across the lake is the faint ghost image of an ancient city. If a character steps through the portal, they are drained of 4 constitution points (temporarily) and find themselves on the shore of the Lake of Hali. This is Carcosa.
Once on the other side, the portal is vague and indistinct, detectable as a faint shimmer in the air, like a heat mirage. For the next 24 hours, any wandering monsters have a slight chance of detecting the portal and crossing into the tower. After 24 hours, the portal obscures with mist again and disappears on the Carcosa side; only a Detect Invisible identifies the exact location once the portal has disappeared.
Above the keystone of the arch is a 2' tall bronze metal tablet inscribed with dots and alchemical symbols, resting in a niche.
The Stone Table
Stacked on this 10' long basalt table are 7 bronze tablets, each 2' x 4' and about an inch thick. Carved into each surface is alien dot-matrix script, mathematic and alchemical symbols, and a pattern of random lines and dots. The lines and dots represent a star pattern for the star charts on the next floor, but this isn't immediately apparent to the characters.
The tablets contain the coordinates for calibrating the Gateway Apparatus to open the proper gate. There are 7 tablets on the table, since the 8th tablet, the Carcosa Tablet, is already loaded over the portal. If the party learns how to open gateways and experiments by loading other tablets, here is the list of tablets and destinations. Note: A Read Languages translates alien script and identifies the title for each tablet.
List of Gate Tablets:
1 The Black City
2 The Great Library
3 The Moon
4 Unknown Kadath in the Cold Waste
5 The Plateau of Leng
6 Lightless Cavern of N'Kai
7 The Isle of the Unknown
8 The Lake of Hali (this tablet is already loaded)
[ I may add a brief description for each location. For instance, the Black City location offers a view into the city's past, 80,000 years ago when it was teeming with alien greys and their monstrous servitors. Certainly items 7 and 8 I'll use for my home game, but if this ever reaches print, I'm not sure the etiquette for referencing someone else's published work, it's probably wise to get the author's permission. ]
Behind the stone table is an alcove with a shaft leading up to the second and third floors of the tower. The aliens used levitation to move between levels, but rungs were provided for their earthbound Plastical servitors.
The Gateway Apparatus
This massive arcane machine thrums with nascent power coming up through the floor. There is a trapdoor hatch (orange) nearby that leads to a maintenance shaft running alongside the vibrating power conduits. The shaft leads to the Transit Tunnels (dungeon level 1) and then continues all the way down to the Warrens of Decay (dungeon level 2). A simple set of metal rungs allows descent.
The machine consists of a large switch, a series of five joystick controls, and a large button. The switch turns on the machine, which hums more noticeably. Immediately, the thaumaturgic circles in the nested discs begin to glow with a blue light. Over on the bronze tablet above the portal, the star coordinates also begin to glow.
The joysticks are locked in place. They can be pulled slightly up to unlock them, and the glowing dots on the bronze tablet star coordinates move out of alignment. The portal to Carcosa immediately closes. There are five joysticks, and each tablet has five dots for guiding them into celestial alignment. As the joysticks are moved, the armatures of the machine shift and move, and the view of the night sky on the next floor up shifts to align with the proper constellations.
The large button sets off a cacophony of fluting sounds, chimes, and harmonics from myriad bronze devices hanging off the ceiling. The music sounds discordant, atonal, and oddly mathematical to human ears. The quality of the music changes as the joysticks are realigned to ensure proper harmonics for the summoning.
The aliens used the Gateway Apparatus to unseal portals to other times and places by summoning the Opener of the Way through the music of the spheres. The proper ritual sequence starts with placing an appropriate bronze tablet above the portal. A living sacrifice is manacled to the sacrificial stone in the inner circle. The machine is powered on with the large throw switch. The joysticks are used to align the projected lights on the tablets with the celestial dots on the tablets, and the joysticks lock into place. On the second floor of the tower, the view of the night sky shifts to the correct celestial quadrant, though this isn't readily apparent from the first floor. Five ritual contributors step onto the five points of the star and place their hands on the crystal orbs. The button is pressed, and the "music" of the spheres begins to reverberate through the room.
The ritual can take 5 to 30 minutes of the atonal music before the Opener of the Way, an avatar of Yog Sothoth, arrives. For every 5 minutes of ritual time, a spell level of magical energy is drained by the orbs, or a point of wisdom (temporary ability score loss) is taken from one or more of the contributors. If the ritual takes 25 minutes, 5 total points of spell levels or wisdom are taken by the orbs. A single caster could contribute three 1st level spells and a 2nd level spell to meet the entire requirement, or it could be apportioned amongst all the contributors. When the Opener of the Way appears, its a bizarre globular monster composed of silvery spheres - it materializes in the central thaumaturgic circle. Standing in the presence of the Opener of the Way is terrifying, and the characters at the orb stations must make a Save vs Spells to avoid falling away in fear.
The Opener of the Way is fully formed after about 5 minutes, and the new portal opens. The Opener consumes the sacrifice, absorbing the victim completely (treat as disintegration). The machine is safe to shut down, dispelling the Opener. If no sacrifice is offered, it grabs for any character that abandoned an Orb station before leaving; if none of the stations were abandoned, a random character is selected from those standing outside the magic circles. A Protection from Evil spell wards a character outside the thaumaturgic circles.
Through trial and error, players may discover the proper sequence to align the machinery and summon the Opener of the Way.
The Opener of the Way
[ Omitting stats for the avatar of Yog Sothoth, the All-in-One ]
That's the first floor, at least...