Not every place in the ruins will be immediately accessible to low level characters - unreachable areas create mystery and give the DM space to expand. My last Black City post introduced The Black City Construction Company - making areas inaccessible by placing some Watchers near them to drive away characters not carrying the proper passkeys or who don't have sufficient power to knock out a stone golem.
I'll be putting up some brief descriptions of the proscribed areas, but these areas won't actually get mapped or stocked until later in the campaign. Please don't mind the prosaic building names, the players will never know what this stuff is called, anyway.
Note: the letters F and B correspond to lettered areas on the city map, and you can keep up with the project from the Black City project outline (and the page up above).
F Central Command
Central Command is a domed, shielded building warded by a pair of Watchers (blue passkeys to pass). Inside one can find a large map projection of the island of Thule on a holographic sand table, including a red blinking dot pinpointing the location of a crashed alien ship buried beneath one of the glaciers. It would be a fun side quest out of the city to find and excavate an alien ship, and it could introduce a bizarre new monster (Alien, The Thing) or a new race - like the Reptoids. (The players wouldn't know what the blinking dot represented until they went there and dug it up).
Central Command features a number of arcane machines and "computers" that the characters can access, inadvertently turning on or off some of the still functioning defensive systems in the city, like the Face in the Ground. It was once home to the psychic antenna of the Hive Mind (Cerebro?) that augmented its telepathic communication in the city.
Central Command is also the place from which the Beacon emanates. When the Grey race died in a mass extinction, one of the last conscious acts performed in Central Command was to activate the Beacon, a massive signal beaming an SOS message into deep space to contact other Grey colony ships.
No rescue ship arrived, but many deep space organisms inimical to earthly life have followed the Beacon down to earth over the millenia; some have even established lairs in the frozen city. (You'll see them referred to as Star Demons or Space Devils in the area descriptions). One of the most dangerous of these Space Devils lives in the Palladium, letter N on the city map.
The Beacon still functions today, blazing it's radio signal into the sky. Characters with ultravision can see it clearly, and it lights up the city like a searchlight for monsters with ultravision.
B Tower of Astronomy
The Tower of Astronomy is a twisted spire of impregnable rock in the southern part of the city; a long stair climbs to the sole entrance, where a pair of Watchers flank the door making attack nearly impossible. Green passkeys will allow access past the doors. The Tower was used for charting the stars and exploring other times and places. The Greys watched the stars carefully, using the stars to select the proper celestial alignments for opening dimensional portals.
Inside, there are telescopes, star maps and 3-dimensional representations of the solar system and galaxy (mind-blowing for Vikings!) and the opportunity to see into other times and places - including the past and future of the city itself!
Portals and visions feature in many Lovecraft stories ("The Shadow Out of Time", "The Haunter of the Dark") and I like the idea of giving the players a glimpse of the city's alien past.
Next up - the remaining sealed areas - the Institute of the Arcane, the Great Plaza, and the Spire of Thaumaturgy