Let's get this straight: You do not take a stroll for the exercise. If burned calories are all you're after, the results of a stroll will make you cry. No, you take a stroll to clear your mind, to work through whatever knotty problem currently plagues you, or, if you must take a companion, to have a serious conversation. (Sadly, this also makes a stroll a perfect occasion for a breakup.) A stroll is like meditation for those of us who lack the balance — both mental and physical — to sit for hours in the lotus position. The ideal stroll should not be challenging or interesting enough to distract you from your own oh-so-important deep thoughts. Which brings us to the Missouri Botanical Garden. Set on 79 acres in the Shaw neighborhood, MoBot offers miles of paved paths for your strolling pleasure, through woodlands and apple groves, a Japanese water garden and an English maze. The plants are pretty. They smell good. If you get weary — from the heaviness of your thoughts, naturally, not from the act of strolling — there is always a shady bench where you can plop yourself down and pull out a nice, diverting book. Best of all, the gardens are open every day, even in the winter, and on Wednesday and Saturday mornings St. Louis city and county residents get in for free. Because contemplation ought to be the only luxury that costs nothing.