Grab yourself some grandmaster gear via this quest line.
The Witcher 3: Blood and Wine - Master, Master, Master, Master
This quest sees you go and visit a master smith who can create the finest armour - but he needs a hand. You'll want to be around level 40 thanks to some of the beasts you might optionally encounter during this quest line.
After obtaining the quest from the notice board in Beauclair, the capital of Toussaint, head to Lafargue, the previously mentioned smith.
When you meet him, you'll want to ask him about the five Witchers who vanished and their gear. Their equipment all matches up to the various schools of equipment Geralt can himself use. Then ask about the contract - obtaining diagrams on how to build some of the gear these Witchers used.
In doing this you'll open up five new Treasure Hunt quests spread across Toussaint. These are all Scavenger Hunts - one each for Grandmaster Feline, Ursine, Griffin, Wolfen and Manticore gear.
In order to complete this quest you'll want to complete one of these treasure hunts. They're all broadly the same: each will have you finding multiple parts of a blueprint in order to piece the story of the Witcher behind it together.
All of these quests are of course subtly different, but generally speaking they're also broadly the similar enough - each will see you travel to a location, engage in some battles and then search bodies and hiding spots for loot in order to find the blueprints.
You'll usually be redirected around by clues several times before finding all the parts needed, but there's no major boss encounters and so it really boils down to following waypoints, fighting and looting. Simple.
When you've found one complete set and thus completed one of the Treasure Hunt quests, return to the smith. He'll take them and thanks to them be able to craft Grandmaster gear of the type you returned the blueprints for. This will mark the quest as complete and grant you the rewards, but you can also return the remaining four if you so wish - their treasure hunt quests will remain in your log.