AoE: Castle Siege - Which buildings get hidden during an attack?

One of the most important things to consider when playing Castle Siege is the resources you'll spend on defences. Additionally, this means you'll have to carefully place walls and fortifications to defend all important buildings. However, I have noticed that when a player attacks you, some buildings are not visible to them (e.g. the army camps). Considering that they do not see them, it is useless to protect them and waste precious wall hubs on them.

Therefore I was wondering which buildings are visible to an attacker and which aren't. The ones that aren't can then be put far away in a corner.

I am guessing that the following buildings are hidden, but I am not sure:

• Army camps only