These complicated conundrums provide an amazing brain workout. To solve a lateral-thinking problem you have to throw out assumptions, think out of the box, and look at the clues from a new perspective. It's all a matter of training the brain to think more creatively. Here's an example of one tricky little mystery: A foreign visitor to London wanted to ride up the escalator at the subway station, but did not do so. Why? Could you guess the reason is...