Palace
Every level speeds up all your construction.
The palace is the mind of a holding. In its stone courtyard scribes keep the records, foremen wait for orders at first light, and messengers ride out of every gate at once. Every wall that rises in the city, every road that opens, is reckoned here first, over a long oak table.
As the palace grows, the holding quickens, for work no longer runs on shouting but on order. Every great kingdom in history was first founded at the head of a table.