I suppose it might be Kasperle auf Burg Himmelhoch
by Josephine Siebe. I've known that book since my early childhood days when my dad first read it to me. He already read the Kasperle books in his childhood, they're that old. But they're simply funny and amusing and lighthearted and this is the one I remember best so I suppose it's the one I read most often. I'm a sucker for anything that will make me laugh. I should read it again soon, especially as I now have it on my kindle... but we still have the old hardbacks downstairs in the cellar, too.