Here is an idea, special cities:
City of Wind:
Has a chance at the beginning of the game of spawning on a peak under the barbarian's control guarded by some flying units (quantity depends game difficulty). The city can only be attacked by units that can move though peaks.
The city cannot work tiles, all citizens are specialists. Population consumes 0
and will grow until the city becomes too unhealthy. City cannot produce units (maybe only flying units), only buildings. May have some other special features making it worth capturing.
City of Water:
Can be built by creating a world settler boat unit (requires water mana). Settler can build a city on any ocean tile. The city may only work ocean squares (no coast squares) and gets 2
1
2
(including the food from a free lighthouse). The city has a chance of moving (along with all units in its square each turn) to an adjacent square.
City of Fire:
Wonder that can be built by evil civs when the Armageddon counter is at least 40, requires fire mana. It spreads the hell terrain and grants -1
, +1 fire affinity to units created.
City of Earth:
Build a special settler unit (requires earth mana), that when a city is created can use work tiles that is also being worked by another city. This city can also work tiles that are owned by an opposing civ, or are occupied by a hostile unit.
City of Wind:
Has a chance at the beginning of the game of spawning on a peak under the barbarian's control guarded by some flying units (quantity depends game difficulty). The city can only be attacked by units that can move though peaks.
The city cannot work tiles, all citizens are specialists. Population consumes 0

City of Water:
Can be built by creating a world settler boat unit (requires water mana). Settler can build a city on any ocean tile. The city may only work ocean squares (no coast squares) and gets 2



City of Fire:
Wonder that can be built by evil civs when the Armageddon counter is at least 40, requires fire mana. It spreads the hell terrain and grants -1

City of Earth:
Build a special settler unit (requires earth mana), that when a city is created can use work tiles that is also being worked by another city. This city can also work tiles that are owned by an opposing civ, or are occupied by a hostile unit.