On my YouTube channel I've created a gameplay walkthrough video covering the first hour of this game.
In short, for those who want to avoid all spoilers, this unlocks once you are sorted into one of the four Hogwarts houses. The achievement is unlocked at about 50:15 in the video, which lets you know the opening and tutorial for this game aren't short.
For those who wish to know everything you have to do before unlocking this:
*** Spoiler - click to reveal ***You'll create your character, receiving your Hogwarts acceptance letter, meet Professor Eleazar Fig and Mr. George Osric for a cartridge ride, unlock a magical container to find a strange key, have a close encounter with a dragon resulting in a portkey escape, explore an island in the Scottish Highlands leading to ruins, find a magical doorway leading into the depths of Gringotts, enter vault twelve and solve its puzzles, learn the spells Revelio, Lumos, and Protego, look into a Pensieve at memories of a wizard from hundreds of years ago (Percival Rackham conversing with Charles Rookwood), have a standoff with Ranrok who appears to be our big bad of the story, escape during a chaotic battle with a guardian (not sure of its actual name), and arriving at Hogwarts late for the Sorting Ceremony.
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