We are used to telescopes as instruments on Earth looking out on space or instruments in space looking at even more distant objects in outer space. The Einstein Telescope is very different and will be build deep under the surface of the Earth. Over 2,000 researchers participate in the international organisation and there is a competition between different countries about where to build it. One of the researchers who are involved is Professor Niels Obers from the Niels Bohr Institute in Copenhagen. Niels Obers is telling Science journalist Jens Degett what the new instrument is able to reveal when it is finished? Niels Obers also describe gravitation in Newtonian terms and in the frame of Einstein's general theory of relativity. Both descriptions are incomplete but due to research with gravitational waves we may reach a better understanding of these phenomena