Humans, unlike other animals that are drawn to water, are not natural-born swimmers. We must be taught. Swimming is an introspective and silent sport in a chaotic and noisy age; it’s therapeutic for both the mind and body; and it’s an adventurous way to get from point A to point B. It’s also one route to that elusive, ecstatic state of flow. These reasons, among many others, make swimming one of the most popular activities in the world. New York Times contributor Bonnie Tsui, a swimmer herself, dives into the deep, from the San Francisco Bay to the South China Sea, investigating what about water—despite its dangers—seduces us and why we come back to it again and again.