Exploring the ‘invisible Universe’ – the mysterious web of dark matter and the dark energy that maintains the accelerated expansion of the Universe – is an ambitious task that ESA is tackling with Euclid, a mission to help us understand these exotic entities, which account for more than 95% of the Universe’s makeup.With XMM-Newton and Integral, ESA is observing rapidly spinning dead stars and hot gas in the cosmic web, some of the hottest and most energetic phenomena anywhere. Future missions like Athena and LISA will enable us to study, for the first time, even more extreme high-energy events – such as colliding supermassive black holes producing gravitational waves, fluctuations in the fabric of spacetim.