These are genuinely difficult mazes, lovingly illustrated. Unfortunately, they all contain a "key" to make the puzzle trivial to solve. There are usually enough hints on the page to find the key, although some of them require knowledge of Latin, and one requires you to know who Karl Marx is. As a child, I wasn't privy to such knowledge, and just looked up all the keys in the answer section. But it's the kind of knowledge that sticks in your mind, so reading it this time I couldn't forget what the keys were for each puzzle. So I decided to search for Heimann's extra details, which kept me busy for a couple of hours - there's a set of objects that's supposed to appear in each picture, like a bird, a fish and a star, and they all also contain a little picture of Australia. ( )