Information about how to obtain the achievement David and Golyat in The Witcher 3 Blood and Wine.
During the Main Quest The Beast of Toussaint - shortly after you arrive in Toussaint, in fact - you’ll see a knight foolishly squaring off with a giant. A giant capable of charging through windmills and tossing horses around. Suffice to say, the knight is overmatched and Geralt, doing what Witchers do, intervenes to slay the monster.
Golyat may be large, but his size belies his surprisingly low damage output. Probably because it’s the first boss in a DLC where characters can start with a relatively underpowered protagonist. This is fortunate, because there’s an achievement associated with killing Golyat with one shot for your crossbow. Assuming you didn’t start Blood and Wine as a standalone and completed the main game, you’ll be aware of the crossbows limitations. Under water, it’s Geralt’s best (and only) option, capable of dispatching Drowners in a single shot. Without being submerged, however, it turns into a peashooter, largely only capable of tickling foes while somehow also being able to knock massive flying beasts out of the sky.
It’s an odd weapon, and at a glance, doesn’t seem like one well suited for a massive, flightless, terrestrial foe like Golyat.
Golyat, in the tradition of mythical giants, has a weakness - his eye. One well-placed shot will fell this giant, a fact which Golyat perhaps is well aware, due to the odd precaution he’s taken. He’s wearing a helmet… well, a barrel, but it’ll still suffice to protect the giant from Geralt’s crossbow bolts. Golyat can be felled like any other monster; striking it with Geralt’s silver sword (perhaps enhanced by Ogroid Oil) while protected from Golyat’s surprisingly flimsy attacks via the Quen sign should see the giant laid low before long, but if you want this achievement, you’ll need to go for the eyes, boo.
Aim at the eye slit in the center-right of Golyat’s barrel helmet (right from your perspective, not Golyat’s right). You don’t need to whittle the giant down or anything, one well-placed shot will fell the monster. Of course, considering the inherent inaccuracy of the crossbow and the fact that Golyat probably won’t deign to stand still while you aim, this will probably be more a matter of repetition and luck than one of accuracy and finesse. Once you put a bolt in Golyat’s eye, however, the giant’s life bar will vanish to the cheers of the nearby knights and you’ll earn this achievement.
Kill Golyat with a crossbow bolt to his eye.