Maribor Gate

From Witcher Wiki

The Maribor gate dominates the view to the north of the town centre in the Outskirts, but offers no easier entry into Vizima than any other gate. The two city guards flanking the gates doggedly stick to their script: show your pass to Mikul, or get lost.

From the Trade Quarter, this gate is no more passable. From inside the city, the gate is also guarded and even more heavily, so I guess leaving is frowned upon as much as entering.