Yes, I can mend your book! You should bring it to the library. Just come right in to the back room and tell Madam Pince you're coming to see me, I'm sure she won't mind.

Maybe it does mean sad, but I think that it means what old Muggle churches were like when you would have hundreds of Muggles in one place. Madam Pince gave me an encyclopaedia article about that when I asked and it seems they were really big and full of people. That would probably feel - strange, to be in such a big crowd.