The Primary Unicomplex is a vast intergrated network of thousands of structures structures and hubs housing trillions of drones spanning 600km in the Delta Quadrant.(VOY - Dark Frontier) Transportation is possible from one hub to another without the use of transporters via the transport rails which house small transport vessels and act as a form of road throughout the Unicomplex. The Unicomplex and all intergrated subsctructures are all construted from the Borg's single primary alloy tritanium, there are also additional Unicomplex's spread throughout Borg space. The purpose of Unicomplexes is primarily of Collective's knowledge aswell as acting as a gigantic relay which receives and processes the hive mind signals from the thousands of Central Plexus' from each ship across the galaxy, assimilating all the information received, storing it and re-distributing it across the entire Collective. The central hub of Unimatrix 01 houses the Borg Queen's lair in which she may dock or undock using her Borg Diamond vessel for rapid deployment to another part of the galaxy. Unlike other races the Borg do not require shipyards to construct their vessels - instead they simply upgrade assimilated vessels to one of the classes of Borg vessels (ENT - Regeneration).
The central hub of the Unicomplex possesses a vast sensor grid covering the entire Unicomplex and its own tractor pulse capable of holding vessels detected within range (VOY - Dark Frontier). However it is otherwise completely defenceless, relying upon the hundreds of vessels, mostly cubes to defend the structure in the event of any form of incursion.