S.P.E.W. stands for Society for the Promotion of Elfish Welfare. In order to learn the Alohomora spell from her, players need to travel to Hogsmeade (which is another beautifully recreated area), and put up S.P.E.W.
The most prominent example of this is one of the early missions players receive from Hermione.
Every single area of the castle that appears in the films is recreated in this world, but what is truly interesting to see is that there is a breadth of elements to the game - locations, missions, or even props on classroom tables - that are direct references to Harry Potter lore that never made it into the films.
