Bricksburg is one of the many realms of The LEGO Movie based off of the Town and City themes.
Bricksburg is a realm composed entirely out of one massive city inhabited by many with city-related occupations, like barristas, construction workers, business men, and others. During the reign of Lord Business, walls were built around the city blocking it off from the other realms and all of the inhabitants who were caught building against the instructions were "put to sleep".
Cameras placed all over the city watch citizens to make sure that they follow the instructions. Like the other realms, the Master Builders built tunnels in the massive walls surrounding the realm in order to escape President Business's grasp.
It was also the first (and only) realm to be attacked by the Kragle-izer until President Business was redeemed and un-kragled the affected parts of the city.