Harry had pored over books, searching for better wards than he had set up around his own cottage. The wards around his and Ginny's home back... well, back home, were quite extensive, but he hadn't been the only one to set them up. He would, however, recognise them.
He might've felt ridiculous bringing the book of house wards to Cassandra's cottage if he'd cared what others thought of him, but thankfully, that wasn't a problem. He couldn't simply put the wards on her house without her approval, not to mention showing her how to take them off. Then there was the issue of not knowing how to put them on without the book's instructions, and the book was definitely coming with him.
Keeping an eye on Grindelwald's cottage, Harry turned into the short path leading up to Cassandra's. He would go see him later, when he knew Albus would be away. It was for the best.
He knocked on the door, announcing himself through the wood.