The River Derwent has a mesmerising quality that draws many of us in regularly, but for the past five years it has fixated artists David Stephenson and Martin Walch. The pair recorded a remarkable 2.5 million images of the river as part of a project on show now at the Tasmanian Museum and Art Gallery. In our cover story, the men share their adventures along the river that defines Hobart and is a huge part of our everyday lives. “It’s the source of life, isn’t it,” Walch says. “It’s hard not to sound a little bit cosmic, because it’s a really big system that keeps a lot of things alive. Without it we’d be much poorer.” Also this week, we get all alert and nervy over caffeine. Is it good or bad for us? How much is too much? Why is coffee so loved that 500 billion cups of it are drunk worldwide each year? And would we be better off taking power naps at work rather than trying to super-charge our way through the day with instant, espresso and latte?