Berlin is a rather large city, obviously, and there are multiple areas where magical shops are hidden amongst the rest of the Muggle shops, but Müller Street is the best place to go to find just about everything one could need all in the same place. It is rather easy to get to. It is located in east Berlin's Mitte district. Magical folk will see a door in the side of what otherwise looks like just an old brick wall, half crumbling and there for no good reason. Walking through that door will take you to Müller Street, with all manners of shops -- for pets, potion ingredients, cauldrons, and more.