[Fantomen]

I like the idea of a big castle production bonus, but that means all forts need to be expensive or it might get overpowered. In the example above you could exploit the hill forts in swamp and forest for example. Better to have swamp fortress and forest citadel. Other than that I like stavis suggested list.

Too bad you can´t assign the prodbonus only to one fort type to encourage the player to build in mountains.