What is a good mid-game achievement in STALKER 2?

TL;DR giving the game as a present to my dad on Christmas, but he generally doesn't game that much due to other responsibilities (with STALKER being one of the only exceptions).

As such, I wanted to set him a goal to work towards in the coming months which isn't necessarily end game. but which you have to put a fair amount of effort in to achieve (and which you don't have to go massively out of your way to achieve).

Since I know little to nothing about the new game, I want to check whether anyone knows of a sufficient achievement/stage of progression which you feel would mark when a player has got around hallway into the game in terms of progress?

I would prefer targets/goals which don't spoil the story or particually cool mechanics which people feel are best discovered by the player.

Edit: Achievement is being used in terms of it's actual meaning, not a specific steam/GOG achievement system.