Thurstle Island: Ziggurat of Yog

Another Post-it Map

The landscape of Thurstle Island's City of the Ancients is pierced by many towers. Among these is a sinister 200 meter black stone ziggurat. 

Five layers rise into the sky, and a single steep, narrow stair climbs to the pinnacle. The rise of the steps is much to high for a humans foot, and their breadth is very narrow. There are no railings to prevent a lethal fall. At the top, there is a shrine and a shaft that descends all the way down, through the structure, and into the earth. 

This is a small, fairly linear dungeon with a couple minor fights and some obstacles on the way to meet an Elder God and claim a dubious treasure. It should take about one session to run.

How It Works

The Climb

Climbing the stairs is hard, dangerous work and should exhaust would-be explorers. 

Roll for an encounter for each tier. Possible hazards: 

1. Flying predators (stirges, mi-go, I'll probably use baby rocs)
2. Wind: Strength check or near fall. Lose some equipment. 
3. Cold blast: Constitution check or advance on Deprived track.
4. Sky Blackens. Finish the climb in darkness.
5. Sickly premonition: Someone has a strange vision.
6. Rivals are ascending from below.

The Shrine Gate & Ritual Oubliette

A pentagon shaped structure. The entrance is on top.  Inside, the walls slope toward a hole in the floor. 

Ancient glyphs (readable by any competent magic user) on the walls. Most prominent among them Humble, Descend, Caution, Worship, Offering. 

Vandalized Nihei

The Ritual Oubliette:

• A dark hole descends all the way through the structure into the ground. It's a drop of >200m. 
• It's scary but there's a deceleration field active in the shaft. Falling won't cause serious damage.
• The shaft leads into the Observatory. 

The Observatory

The observatory hangs under the ziggurat in a sphere of hard vacuum. This will not be immediately obvious to those inside the observatory. 

• Hatch Up: The observatory can only be entered via the ziggurat's oubliette shaft.
• Armillary: Fiddling with this device will grant creepy premonitions. If you have a system for fortune-telling, this is a good place to use it.
• The sacrifice room dominates the upper level of the observatory. When visitors arrive, the doors to the other rooms will be open and the golden doors to the outside vacuum will be closed.
• The doors into the room show glyphs:  Person, Gift, Threshold, Lurker, Call.
• Golden doors show the glyphs: Void, Gate, Key, Beyond, Outside
• The wall between the observation deck and the sacrifice room is made of glass. This room contains a bank of levers that control the sacrifice room doors.
• The door to the vacuum cannot be opened until the doors to the interior rooms have been closed. 
• If closed the interior doors cannot be reopened until the outer vacuum door is cycled. 
• When the outside door is opened, the contents of the sacrifice room are sucked out.
• Quick action can close the door before the room is completely voided.
• The hatch down will be closed until a living person is sacrificed to the void.
• Green slimes, degenerated former servants of the Ancients, lurk, looking to consume any living thing that trespasses the observatory. I have a whole post about these. They are nasty.
• The shrine contains numerous inscriptions which grant clues to the purpose of the facility and who it is designed to contact. Sincere efforts at respect and self-abasement might confer a minor blessing.
• The communication room's walls and floors are made out of glass, looking out on the void.
• It will not be immediately obvious, but this room is the exact same size and shape as the shrine on top of the ziggurat. 

The Ritual

Art by Damsa

This ziggurat exists as a means to contact Yog-Sothoth. 

"Yog-Sothoth knows the gate. Yog-Sothoth is the gate. Yog-Sothoth is the key and guardian of the gate. Past, present, future, all are one in Yog-Sothoth. He knows where the Old Ones broke through of old, and where They shall break through again." - H.P. Lovecraft

 Contacting old Yog, is foolish but also fun. This is the DM's chance to role-play an Elder God.

• To summon Yog, a living person must be vented into the void sphere that surrounds the Observatory via the golden doors in the sacrifice room.  This opens the hatch down to the Communication Room. 
• Yog appears as a collection of glowing spheres, lighting up the void. He will speak into the minds of everyone in the communication room. 
• His utterances will be esoteric and difficult to interpret but generally curious and friendly. Role-play him to be unnerving but also helpful. This could could go a lot of directions.
• Yog is generous but everything he offers comes with unexpected consequences.
• Unless the players are rude, at the conclusion of their conversation, one of them (a mage or cleric probably) will find that they have an arcane tablet in their hands (how it got there is inexplicable). This tablet has a Safe Portal spell.
• Safe Portal spell: This spell will only work if the caster is in imminent danger, and will create a portal to somewhere familiar and safe (but not of the caster's choosing). Effectively a Scroll of Town Portal. When cast, the DM will choose where it goes. The side effect, that will not be obvious is that this portal is permanent and passable by any creature that fits the physical doorway. When cast, it will link a dangerous dungeon location to the middle of the characters favorite tavern or a close friend home. The adventurers are somewhere safe, but the danger will likely follow. Oops.
• At the end of the conversation, the light will fade and the glass to the outside will go dark. 
• When the characters exit the room, they will find themselves on top of the ziggurat leaving the shrine (which is a replica of the communication room), rather than returning into the the upper level of the observatory.

Design Notes

This is a weird dungeon. It's got a puzzle and a couple minor fights, but it's core is a strange role-playing encounter and the set-up for a weird treasure that could have a big impact on the future of the campaign.

I think this structure could be re-located fairly easily to another dungeon, but I'm not sure if running this kind of session is of interest to other DM's. I'm very curious what you all think and would love to hear your thoughts.