Well, I messed up. The guards denied me entry at a gate on the road to Novigrad, telling me that I need some kind of pass to get through. I bribed the guard, and he told me that someone is selling passes. I talked to the shady merchant, and he told me I'd get one cheaper if I helped his brother-in-law.
I went to the brother-in-law, and tried to help with the monster problem. I managed to kill all the monsters, but it seems the brother-in-law died during the monster attack. The shady merchant didn't take these news very well and I can't get a pass from him now.
Where can I get a pass to enter Novigrad and Oxenfurt now?