Guard Pavilions are tall buildings in which one Guard or one Armed Guard can be deployed. They will patrol on top of the Guard Pavilion and watch over near area, tazers and weapons can be used if needed. There are two types of Guard Pavilions: the normal one and a corner one. They are different in their texture and patrol path.
In order to unlock both, you have to log in into an paradox account in the launcher. After that, you will be welcomed by a popup after starting the game, thanking you for connecting the account and informing you, that, as a reward, the Guard Pavilion has been made available.