On the topic of switching castles to cities and vice versa.

[Kraggenmor]

The only buildings that stay are the ones which are common between both cities and castles. Religious buildings and ports for example.

[dismal]

Might be nice to get the definitive answers to questions on this issue.

Seems to me you keep religious buildings, ports, roads, blacksmiths, brothels, siege buildings, gun powder buildings, and farms.

Not sure what happens going from a city with a level 3 church (abbey) or above to a castle. Presumably you'd downgrade to a level 2 church. (Can you even do this, or is the city too big to convert?) I personally never convert cities to castles.

Not sure about wall upgrades (ballista towers) but would guess you keep them.

I think most of the specialty buildings (plaza del toro, merchant banks, race tracks, etc.) are city-only but haven't played them all enough to be sure.

The question was raised a while back as to whether you automatically get the cash from the buildings that are razed. Not sure if we got the answer to that.

[HoreTore]

Once you have stone walls, you cannot convert to a castle, so the abbey isn't a problem.

The things remaining from a castle-city switch:

Church/masjid
Port
Siege builders
Barracks(not the first level, ie. the peasantbuilder)
farms
Cannonmakers
Swordsmith guild
Crusader guilds

Everything else gets destroyed.

Note that with the barracks, the first city level is equal to the second castle level. So, if you only the first level barracks at a castle, it will be destroyed when you convert.

[sapi]

Why CA took out the 'if you proceed with this transformation the following buildings will be destroyed' (as shown in preview screenshots) is beyond me