Visiting the vineyard
The quest is unlocked automatically during The Beast of Toussaint main quest. For defeating the shaelmaar on the arena on the Tourney Grounds Geralt will receive a gift from Anna Henrietta - act of ownership of the Corvo Bianco Vineyard located in the western part of Toussaint (M2,1). The protagonist will receive the Key to Corvo Bianco and Deed to Corvo Bianco. The vineyard can be visited anytime you want. After arriving there meet with Majordomo Barnabas-Basil Foulty. You can agree for him to show you the vineyard or talk with Barnabas about the possible expansion options.
First set of vineyard expansions
Modus operandi is very simple - you can listen to Barnabus' suggestions about the available projects and then spend your gold to realize them. Each project additionally requires you to wait from one to few days until it is completed. At first you can order three projects:
1) A general renovation of the vineyard buildings - It will cost you 5000 crowns and it will take three days.
2) Armorer's Table - It costs 1000 crowns and completing it will take one day.
3) Grindstone - It costs 1000 crowns and completing it will take one day.
Go back to the vineyard after three days and speak to Majordomo again. Barnabas will inform you that from now you can use the weapon and armor stands and you can hang paintings on the walls. Majordomo will also tell Geralt to check the basement (the same where you fought bruxa). Go there and find the weakened wall shown on the above picture. Use the Aard sign to break the wall. You will unlock access to a hidden alchemist lab in which you can break down mutagens and increase your supply of potions and bombs.
Second set of vineyard expansions
Speak with Barnabas about other available projects. The following projects will be available:
1) A new bed for Geralt - the project costs 1000 crowns and completing it will take one day. The new bed provides a vitality bonus (+1000 points, 120 minutes) each time when the protagonist uses it.
2) Additional weapon stands - They cost 500 crowns and you must wait one day for them.
3) Additional armor stands - They cost 500 crowns and you must wait one day for them.
4) Renovation of the guest room - The project costs 1000 crowns and completing it takes two days.
5) Stable renovation - The project costs 2000 crowns and completing it takes two days. Renovated stable will provide an endurance bonus for Roach (+100% durability, 60 minutes).
6) Garden renovation - The project costs 2000 crowns and completing it takes two days. After the garden is completed you can collect rare herbs from it.
Meet with the Majordomo once the renovations are over. You can agree to drink expensive wine with him in order to celebrate the end of the renovations of the vineyard.