Sirius had to nick Remus's wand so he could get to Hogsmeade, and of course he had to apparate far enough away so as to avoid any barriers or protection charms. Then with a poorly cast disillusionment charm, Sirius trudged up the hill to the Shrieking Shack. He'd be so close to getting inside that castle, he realized. He tried not to think about it as he pushed open the door.