On holiday in Croatia, I visited Krka National Park, a landscape of outstanding natural beauty where rivers flow clear as glass and waterfalls cascade between lush forest lands. There are several areas in the park where it is safe to swim, and of course people flock towards them. Seeing so many people soaking in the sun, wallowing together in the water, I am reminded of The Garden of Earthly Delights by Hieronymus Bosch.