A one-shot set in a hospital that may not be sterile-white clean, but it is someplace that has color like a family doctor's office. The color has been physically drained, however, with some bodies littering the halls. Nail and hand prints are present on bodies that don't break skin - people who have lost skin coloration, the light in their eyes, and even sullen faces for the worst of them. They are still technically breathing - but why bother breathing when it's soo much effort?
It looks like this place should be abandoned afterall but the party sees light down the hall. Color on the walls - pictures of wounded but smiling kids, families that have been saved. Yet there are wretched spirits trying to eat at it - 4 armed shades wearing hospital robes or shattered guard armor. Blue tinted skulls with horrible red abyss for eyes and mouths clawing and scratching at the light.
Interrupting these shades introduces the party to the main npc, the Last Light Nurse. She is doing her best to care for the men women and children still stuck here. But she can't leave here, not yet - not until this place has been laid to rest. It's up to the party to find a number of light sources - memories - made from determination, love, care, compassion. Stuff that people oft forget, but are so important to have. Fighting back against the Unkillable darkness and helping to purify the place will transform this dark sterile hospital to an overgrown grove, where only then it's revealed the last light nurse is an Azerai / Ziggurani of healing, and you were essentially assembling her core. An altar of the last patients that were treated here.
Environmental effects include all light sources dimmed, darkvision reduced. Any physical attacks on players reduce attack rolls by 1 each time, For like every 3 attacks maybe a level of exhaustion. Or disadvantage on mental checks.
Rewards?
One could be the option to grab some of the toys or offerings to take with. Players could leave them at healing churches or hospitals anywhere in Unknown, literally able to spread the Azerai / Ziggurani's influence, healing, and care.
There would be a further info dump on Azerai.