Possible things that the phrase "City of Skulls" could mean:

-An essentially normal city--somewhere in middle europe/eastern europe. Each family has, in their home, in a box in the living room, a skull. The skulls are the skulls of the 8,000 defenders of the town, left over from a medieval battle against the Turks, preserved by complex herbal means. The skulls are consulted at important moments--before marriages, births, etc. and are believed to have oracular power by the locals.

-It's a weekly three-panel cartoon. The backgrounds are nearly always nonexistent and the characters are simple stick figures, but the head of each character is a skull drawn with phenomenal and gory realism--cracks in the jawbones, maggots crawling through the eyes leaving trails of blood, etc., that subtly alters panel by panel. Dialogue is phenomenally banal.

Panel 1: "Hey Chris, how's it goin!"

"Awesome! How're you?"

Panel 2: "I'm fine! Gonna go see 'Matrix 3' with mah lady tonight!"

Panel 3:"That's awesome! Have fun!"

Strip runs every week for years.

-It's a tiny city, belonging to ant-sized men. Or intelligent insects. It's built inside the skulls of normal humans, lying by the road. The inhabitants periodically use their cunning to create violent misunderstandings between ordinary people in order to generate fresh skulls and increase their liebensraum (did I spell that right?).

-(sub-idea from that idea: humans live on a planet made of bone--it is actually the skull of a god.. The humans urbanize it completely. They need another planet but have limited space travel. they have to lure enormous beings, spacebeasts as large as Jupiter, and slay them in order to build room for themselves.)

-(sub-idea off that idea: Hormones are not mere characteristics of life. They are a microscopic sentient parasitical or commensal species unto themselves--they subtly encourage specific human relationships in order to allow them to feed off of certain human secretions and complex emotions: post-epic-romantic despair, platonic jealousy, self-righteous enjoyment of one's own loyalty in the face of essential casual and low-level lust.)

-It's a city whose buildings are all carved from a pile of skulls and bones left over from an epic battle, in the dim past, between two armies of colossal giants. Their blood nourished the soil, their bones provided shelter to the earliest humans.

-Two hour commercially-released film. Ordinary guy, driving long distance, happens on a city--maybe Des Moines. Everything is normal except everyone is a skull instead of a complete person. They talk and act like normal people, and can move around and go to work and do stuff, it's just they're skulls.

skull:"Hey, what can i do ya for...?"

guy: "Ummm.... "

skull: "Burger? Shake?"

guy: "Uh...yeah..sure...uh,,,are you feeling ok?"

skull: "Never better! Want fries with that?"

guy: "Uh...o....k..."

girl skull:"Hey Al, whose this tall drinka water?"

-a city similar to actual vernacular architecture in parts of northern africa--carved in rounded domes from pale stone with round windows into a hillside. looks from a distance like a pile of human skulls.

-A city. Everything is made of skulls. Everything. Religious beliefs of locals exclude inventing or employing any technology unless it is specifically derived from the headbone of a once-living animal. Hunting parties in babboon-skull helmets carrying goatskull horned weapons hunt strange and exotic new animals across the bone-strewn planes to harvest new and different kinds of heads. Philanthropic-minded biologists bioengineer new animals so they can kill them and use their skulls for tires, pie-plates, windows.

-(sub-idea: a city of anti-vegans. everything and every product and technology must include some living organism in it. a cross between Existenz and the Flintstones. Televisions are packed with cultures of colored bacteria that change configuration in response to carefully modulated shocks from electric eels of different lengths, sizes and frequencies, creating different images.)

-a city. one of a series of small cities maintained in a secret locales by some country's government. (ours, the russians, some paranoid theocracy, whatever). Each city is a fantastically cruel experiment in biological or psychological warfare. The inhabitants are so extensively and expertly drugged and information-controlled they go about their business--drive, deliver mail, etc.--without knowing what's going on. In The City Of Skulls, the people have no eyes or noses and smile all the time. In the City of A Thousand Pities every child is nailed to the floor (hand hand foot foot) of the family room and ritually humiliated for 6 years as soon as they are born. Inhabitants trained to think this is normal. In the City of Maggots, people aren't buried, taboos are implanted against moving the dead once they die. Sites of car wrecks are left intact, roads are altered to go around them, old people die lonely in apartments, the next tenants move in and leave them slumped over their cereal. In the City of Total Panic Always the walls are fluorescent yellow-green or bright orange or cyan or shrieking magenta and Goblyn plays all the time on public speakers and every food is spiked and every light is blacklight. In the City of Degradation each dweller emulates a designated American celebrity from birth, at all times, no matter how poor the physical or temperamental mismatch. You are a Pauly Shore, you are a Mark Farner, you are one of that girl from Friends. Public closed-circuit TVs broadcast motivational speeches made entirely from samples of Madonna talking, encouraging everyone to Pump Up The Attitude. In the City of Bone White Terror, somewhere in the far north, all is normal, but dreams are carefully designed and modulated. In the City of Unbelievably Awful Food the inhabitants have begun, spontaneously and unexpectedly, to devise a wild array of unusual entertainments for themselves--many of them shockingly decadent.