Both the Western Gate into Oxenfurt and the Border Post in Velen are closed and heavily guarded by Redanian troops because of the recent war. Until this quest is completed, you cannot use the main thoroughfares to traverse the Pontar. However, some slightly less orthodox methods are available such as swimming across the river at a safe distance from any border posts. Fast-traveling between signposts on opposing sides of the river is also allowed, even without the necessary papers.
Doing enough of the Baron's quest Family Matters will require you to travel to Oxenfurt, which will cause the baron to provide you with a pass. Also, doing the contract Woodland Beast can net you an official pass.
Journey to the refugee camp on the southern side of Border Post to find a shady merchant. He'll sell you a fake pass for 100 (50 with Axii) or 25 if you help his brother-in-law, Albin Hart, in Bitter Harvest. If his brother dies, the merchant will refuse to do business with you.
Use the pass
Once you have whichever pass in hand, approach one of the border soldiers, show them your pass, and after a bit of banter, you're allowed through and the quest will conclude. You can even use the fake pass at the Western Gate, though the guard there will note it's missing a seal, but wave it off as their people forgetting stuff like this.
- The Redanian army had placed blockades on the crossings of the Pontar, something which at one point proved quite inconvenient to the witcher. The guards refused to let him cross without showing a special pass issued by high command.
- Luckily Geralt managed to get his hands on just such a pass and from then on could cross the Pontar border at will. I hope he did not abuse this privilege, jumping back and forth across the border, making faces at the poor wretches stuck on one side and taunting the guards who had no right to stop his antics. He mentioned nothing of the sort, true, but that's just the kind of thing one might choose to keep to oneself.
- Acquire a pass granting permission to cross the Pontar.
- Use the pass to cross the Pontar.
- Thou Shalt Not Pass is a reference to the famous line "You shall not pass" from the 2001 film The Lord of the Rings: The Fellowship of the Ring.