I like this month's puzzle on the site:
A hunter leaves his home, walks 10 km to the South and 10 km to the West, shoots a bear, walks 10 km to the North, and is back home. What colour is the bear? You probably know the answer straight away. Now comes the harder question, useful for winning money in bets. The house could be on several additional spots on the Earth; where are these less obvious spots from which a man can have exactly the same trip that was just described (forget the bear now) and be at home again at the end?