Back to Velen
South of the bridge to the Border Post you’ll come across a Shady Merchant. King Radovid V has closed off all the borders into Redania and you can only get in if you have a Pass. The Shady Merchant is willing to help you out for a price.
You can purchase the Pass at the full price of 100 Crowns, ask for another way and then use Axii to lower the price to 50 Crowns, or ask about the other way and he’ll tell you to help his brother-in-law in the quest Bitter Harvest.
If you complete the Bitter Harvest quest then when you come back to the Shady Merchant he’ll drop the price by 25 Crowns.
This is not the only way to get a Pass. The Bloody Baron will give you one at some stage if you follow along with the main quests.