What the achievement asks
Complete 100 hunt steps. Ten points, account-wide.
What a hunt step is
A Grand Hunt is a chain of stages: the hunting party moves across a zone, each stage is a creature or a small task, and the hunt ends with a boss. Each stage you are present for is one step.
Grand Hunts run in three zones, with eight regular routes between them: eastern, northern and western Ohn'ahran Plains, northern and southern Thaldraszus, and eastern, northern and southern Waking Shores. An active hunt is marked on your map, so there is nothing to search for.
You do not have to fight
Credit for a step comes from being in the area, not from contributing. Fly in when the hunt starts, follow the party as it moves, and the steps tick over whether you are killing things or standing on a rock.
That is genuinely how the achievement is designed, and it makes this the least demanding thing in its branch. The one exception is the boss at the end, which has to be tagged like any rare, and which matters for The Best at What I Do rather than for this.
A hunt runs through a good number of stages, so a hundred steps is a handful of hunts rather than a hundred of anything. Anyone working towards the thirty bosses of the achievement above will pass a hundred steps well before they get there.
Do all three hunt achievements on the same hunts
The three Grand Hunt achievements in this branch are not separate jobs. The Best at What I Do wants thirty final bosses, Tetrachromancer wants nine companion colours out of the hunt's reward satchels, and this one wants a hundred steps.
Run the hunts once with all three in mind. Turn up early, stay to the boss, tag it, and open the satchel. Running them for one achievement and coming back later for another is three times the work for the same hunts.
Where it fits
One of eleven under Flight Club, a piece of A World Awoken.