In 'Er Was Eens' we get a look behind the scenes of the Royal Belgian Institute of Natural Sciences. We follow a number of scientists during their work at the Institute in Brussels, but we also go on expeditions at home and abroad. In this way we not only see the world in the museum, but also the museum in the world. Just as science is changing rapidly, so is the Institute. It moves between tradition and modernity, between applied and fundamental research, between small and big questions.